why sing the Mass?

Tl;dr, just read this bishop’s work, https://www.catholicsun.org/2011/12/15/liturgical-music-as-participation-in-christ/#:~:text=Participating%20in%20the%20Mystery%20of,liturgy%20and%20in%20our%20hearts. who has put together everything here in a shorter, nicer way.
NB, the above is only part 1, to read the whole thing at once, see here https://www.catholicculture.org/culture/library/view.cfm?recnum=9963

You might also start with this one for an expedited more legal/practical look at what the Church instructs us to do https://adoremus.org/2017/01/ever-ancient-ever-new-implementing-musicam-sacram-today-part-ii/#:~:text=Musicam%20Sacram%20maintains%20this%20distinction,congregation%E2%80%9D%20(MS%2028).

Why I sing the Mass so much. Resource list and talk
All emphases added
Table of contents:
Scripture on singing in worship
Church documents
A link to the rest of the titles, along with their own links for easy access
Pope’s and Saints teaching on the subject
Further resources of various origin and angle, e.g. bishops, contemporary theologians, parishes
My own, personal example and words

Scripture on singing in worship
The first mention of singing, the first canticle, what pope Benedict XVI called a sort of proto-psalm, is the song of Moses and Miriam upon crossing the red sea and the drowning of the Egyptians in Exodus 15
The whole book of Deuteronomy is explicitly a song God told Moses to write down and teach to the Israelites, so that they would remember it (see Deut 31)(music helps memory like few other things can. And perhaps the rest of the Torah is meant to be sung as well).
Deborah sings at seeing the victory she prophesied (Judges 5)
Hannah, the mother of the last Judge, Samuel, sings praise to God for his birth at hymn which prefigures Mary’s own Magnificat (1 Sam 2:1-10).
The women of israel sing David’s praises upon his victory over goliath (1 Sam 18:6-8) and this song gets well known (21:12, 29:5)
Then David truly blossoms. In artwork, he is recognized as a crowned king with a harp because he wrote the first, and so many, psalms. Every psalm is a song*, and some of them are included right in the narrative books of his life, e.g. 2 Sam 22.
The occasion of the bringing of the Ark of the Covenant into Jerusalem is one of the most joyful scenes in the Old Testament, and so it is naturally accompanied with much singing and music and even dancing (1 Chron 16).
Even before that though, as well as the Temple, David established singers for singing praise to God already while the Ark still dwelt in the Tabernacle (1 Chron 6:16).
After David’s death, Solomon built many grand things, beginning with the Temple. At its dedication, he personally oversaw the worship, and helped make countless offerings, and led a great prayer of dedication. And at the end, much music filled the air, and the singing of psalm 118. Then the shekinah, the cloud filled with the glory of God, which led Ancient Israel through the red sea and the desert, again appeared and filled the Temple.
This dovetails with perhaps Israel’s greatest military victory of all time. When they were entirely outmatched and outnumbered by a coalition army of over 100,000, they actually prayed at the temple as Solomon prayed God would grant at its dedication. Men, women, and children, even babies all prayed, and God answered according to that plea, telling them to march out to meet the huge empire conquering army and that He would give them victory against all odds. Receiving this great prophecy, they bowed down in worship and broke out in song. (2 Chron 20:19) and the next day, with their little army mustered, the musicians of the temple led the way to the battlefield, singing the great Easter hymn, Ps 118 (20: 21).
After generations of abuse and failure and falling away, a good king, Hezikiah arose, and undertook to purify the Temple and restore the authentic worship of the Lord. It was a huge job, and a key part of it was the singing of the psalms of David and those of another psalmist who had since written, named Asaph. (2 Chron 29:26-30).
Young King Jehoiada, who barely survived an insane and evil purge, had also done this on a smaller scale as he took back his throne and the priests cleansed the temple (2 Chron 23:18).
This also was done after the exile, when they rebuilt the city and temple. (Ez 3:11. Interestingly, the psalm explicitly quoted is again, 118) Certain priests and levites job was expressly to keep up the sacrifice of praise, the singing of the psalms, as had been established when the first Temple was built (Neh 12:8, 24,27) as it was “in the days of David and Asaph” (12:46).
Tobit concludes his life at the end of his book with a gorgeous canticle after the archangel Raphael reveals his true identity and commanded them to do (Tobit 12:6, 22; 13).
Judith, a powerful type of Mary likewise concludes her story with a strong song (Judith 15:13; 16)
Key to the prayer of Mordecai for deliverance from death is drawn from the psalms, ‘rescue us, so “that we may live to sing praise to your name.” (Esther 4:17).
So pray (almost verbatim) also the Maccabees on their campaign to liberate Israel (1 Mac 4:33), singing, (again) psalm 118 (1 Mac 4:24) and they explicitly recall and draw strength from the words of the song of Moses (2 Mac 7:6). At another battle, they charge while singing hymns and put their enemies to flight (2 Mac 12:37). In one of their victorious entries, they sing hymns and songs of praise (1 Mac 13:47, 51), and especially when the temple is purified (2 Mac 1:30, 10: 7, 38).
*every psalm is a song, and besides that, psalms 7, 8, 9, 13, 18, 21, 27, 30, 33, 40, 45, 47, 51, 57, 59, 61, 65, 66, 68, 69, 71, 75, 78, 81, 89, 90, 92, 95, 96, 98, 100, 101, 104, 105, 108, 119, 135, 137, 138, 144, 146, 147, and 149 all explicitly mention singing, most of them exhorting it, many of them repeatedly. 137 in particular identifies a lack of singing and end to music as essential to exile, “oh how could we sing the song of the Lord on alien soil?” To be without song for the Lord is to be far removed from Him. Of all the books in the old testament, Jesus quotes the psalms the most, and when he does so, he does it saying things like, ”
Eccelisasties/Qoheleth uses the image of “when…all the daughters of song are quiet” as one of the many signs of “evil days come. And the years approach of which you will say, ‘I have no pleasure in them’” (Eccl 12:4, 1).
Need I mention the Song of songs? It is so obvious, its very title gives it away almost as much as the title psalms (songs) does. And its content is the mystical center of the scriptures, God’s ultimate plan, to wed himself to humanity, for us to be full of love, in marital union with God Himself. How could one merely speak about that? No, the words are poetry and song, the very heights of language and image and expression.
Wisdom hearkens back to the first passover, which concludes with hymns (psalms) (Wis 18:9).
Sirach wisely extols singing (Sir 39:15), names song as part of the wonders which made Solomon so astounding (47:17) (1 Kings 5:12 numbers them 1005!) and recalls re-echoing hymns as part of the glory of the worship led by high-priest Simon in the time of the Maccabees (50:18).
And the prophets have much to say:
Especially Isaiah with about 20 mentions, almost every one in separate chapters, and exhorting the reader/listener to sing out the praises of the Lord. Some of them are songs themselves, like the crucial prophecies in the Songs of the Suffering Servant (Is 5:1, 12:5, 14:4, 7, 23:15-16, 24:9, 14, 16, 26:1, 19, 27:2, 35:2, 6, 38:9, 42:10, 44:23, 49:13, 51:3, 52:9, 54:1, 59:12). Many of the most popular modern hymns are based on verses from Isaiah.
Jeremiah gets one mention very similar to Isaiah’s (Jer 20:13), and twice prophecies the end of song of joy, gladness, bridegroom and bride as part of the punishment due to israel for its evil (Jer 16:9, 25:10) but later prophecies the same’s restoration (Jer 33:11). Many also believe he also wrote at least one psalm.
Ezekiel is given a song to prophesy (Ezek 21:14-22).
As is habakkuk (Hab 3).
As is Zechariah, which Jesus quotes at the Last Supper Zech 3:7-9).
Zephaniah gives two mentions of singing (Zeph 3:14, 17), and
Zechariah rounds out the Old Testament with one more (Zech 2:14). Both exhort singing with gladness at God rescuing Israel from exile

But that is not all! In the New Testament, The very first song is on the lips of Mary after Elizabeth’s prophecy, the Magnificat (Luke 1:47-56), an utterly masterful drawing from and painting with the words of the Old Testament, but fresh and newer than ever.
Zechariah, mute throughout the pregnancy of Elzabeth with John, follows it up in the next chapter with his own Spirit inspired hymn, the Benedictus, as the very first words he is able to utter after his birth (Lk 1:68-79). Together, from ancient times, the Church has used these two great canticles in her singing of the Liturgy of the Hours (evening prayer and morning prayer, respectively).
Matthew and Mark both importantly record the Last Supper ending not with the 4th cup, but with Jesus and the Apostles singing the Passover hymn before it (the Great Hallel, which is nothing other than psalms 113-118) (Mt 26:30, Mk 14:26).
One of the many times Paul is in prison, he spends the night singing hymns to God with Silas as the prisoners listen. God answers with an earthquake which undoes all their restraints and the doors, and converts the jailer (Acts 16:28).
Paul exhorts the Romans “that the Gentiles might glorify God for his mercy,” to “praise you [God] among the gentiles and sing praises to your name” (Rom 15:9). Singing is key to evangelization.
When discussing spiritual gifts and charisms, Paul speaks of singing in the spirit, but also rationally, with the mind (1 Cor 14:15).
Crucially, and famously, he twice exhorts christians to “[address] one another in psalms, hymns, and spiritual songs.” (Eph 5:19, Col 3:16)
Some great examples of these canticles are given within his letters:
Including before both exhortations (Eph 1;3-14; Col 1:15-20)
Briefly to Timothy (1 Tim 3:16, 2 Tim 2:11-13).
Perhaps in Peter’s letter (1 Pet 2:21-24).
And maybe in Romans (Rom 11:33-36)
But perhaps the most beautiful and recognized is the hymn of Jesus’ self emptying near the beginning of the letter to the Philippians (2:6-11)
James, when presenting fundamental teaching about the anointing of the sick, says that those who are well, should sing praise. James ). Not being able to sing is due to sickness.
Finally, the book of Revelation or the Apocalypse is nothing other than a grand vision granted to John while he is offering Mass on Sunday in his exile. It is a vision of Jesus, and heaven, and what will happen, but all in the context of heavenly worship. It’s what everything past, present, and future means in the light of eternity, which is heavenly life with God, and that life is filled with singing, including the song of Moses (very full circle) but also new hymns, never heard before. And thus the Mass, the Divine Liturgy, is filled with singing, because it is nothing other than a participation in, a copy and more than a copy of heavenly worship, on earth, in an earthly way. “We long to go and be with Christ, for that is far better” (Phil 1:23).

Church Documents. Official law and teaching
Sacrosanctum Concilium
CHAPTER VI [yes, they devoted an entire chapter to]: SACRED MUSIC
112. The musical tradition of the universal Church is a treasure of inestimable value, greater even than that of any other art. The main reason for this pre-eminence is that, as sacred song united to the words, it forms a necessary or integral part of the solemn liturgy.
Holy Scripture, indeed, has bestowed praise upon sacred song [42], and the same may be said of the fathers of the Church and of the Roman pontiffs who in recent times, led by St. Pius X, have explained more precisely the ministerial function supplied by sacred music in the service of the Lord.
Therefore sacred music is to be considered the more holy in proportion as it is more closely connected with the liturgical action, whether it adds delight to prayer, fosters unity of minds, or confers greater solemnity upon the sacred rites. But the Church approves of all forms of true art having the needed qualities, and admits them into divine worship.
Accordingly, the sacred Council, keeping to the norms and precepts of ecclesiastical tradition and discipline, and having regard to the purpose of sacred music, which is the glory of God and the sanctification of the faithful, decrees as follows.
113. Liturgical worship is given a more noble form when the divine offices are celebrated solemnly in song, with the assistance of sacred ministers and the active participation of the people.
As regards the language to be used, the provisions of Art. 36 are to be observed; for the Mass, Art. 54; for the sacraments, Art. 63; for the divine office. Art. 101.
114. The treasure of sacred music is to be preserved and fostered with great care. Choirs must be diligently promoted, especially in cathedral churches; but bishops and other pastors of souls must be at pains to ensure that, whenever the sacred action is to be celebrated with song, the whole body of the faithful may be able to contribute that active participation which is rightly theirs, as laid down in Art. 28 and 30.
115. Great importance is to be attached to the teaching and practice of music in seminaries, in the novitiates and houses of study of religious of both sexes, and also in other Catholic institutions and schools. To impart this instruction, teachers are to be carefully trained and put in charge of the teaching of sacred music.
It is desirable also to found higher institutes of sacred music whenever this can be done.
Composers and singers, especially boys, must also be given a genuine liturgical training.
116. The Church acknowledges Gregorian chant as specially suited to the Roman liturgy: therefore, other things being equal, it should be given pride of place in liturgical services.
But other kinds of sacred music, especially polyphony, are by no means excluded from liturgical celebrations, so long as they accord with the spirit of the liturgical action, as laid down in Art. 30.
117. The typical edition of the books of Gregorian chant is to be completed; and a more critical edition is to be prepared of those books already published since the restoration by St. Pius X.
It is desirable also that an edition be prepared containing simpler melodies, for use in small churches. (Which is what we’re using)
118. Religious singing by the people is to be intelligently fostered so that in devotions and sacred exercises, as also during liturgical services, the voices of the faithful may ring out according to the norms and requirements of the rubrics.

From the first instruction (Inter Oecumenici) delineating how the reforms called for will actually be interpreted does not say much about the place of music, but it does repeat this theme:
59. Pastors shall carefully see to it that the Christian faithful, especially members of lay religious institutes, also know how to recite or sing together in Latin, mainly with simple melodies, the parts of the Ordinary of the Mass proper to them.

Because of the deficiencies of IO, another instruction specifically on sacred music, fittingly eponymously named, Musicam Sacram. It has much to say on the place of music and how to use it in worship:
5. Liturgical worship is given a more noble form when it is celebrated in song, with the ministers of each degree fulfilling their ministry and the people participating in it.[4]
Indeed, through this form, prayer is expressed in a more attractive way, the mystery of the liturgy, with its hierarchical and community nature, is more openly shown, the unity of hearts is more profoundly achieved by the union of voices, minds are more easily raised to heavenly things by the beauty of the sacred rites, and the whole celebration more clearly prefigures that heavenly liturgy which is enacted in the holy city of Jerusalem.
Pastors of souls will therefore do all they can to achieve this form of celebration.
They will try to work out how that assignment of different parts to be performed and duties to be fulfilled, which characterizes sung celebrations, may be transferred even to celebrations which are not sung, but at which the people are present. Above all one must take particular care that the necessary ministers are obtained and that these are suitable, and that the active participation of the people is encouraged.
The practical preparation for each liturgical celebration should be done in a spirit of cooperation by all parties concerned, under the guidance of the rector of the church, whether it be in ritual, pastoral or musical matters.
[skipping ahead just for a bit, it will save time to point out #:
27. For the celebration of the Eucharist with the people, especially on Sundays and feast days, a form of sung Mass (Missa in cantu) is to be preferred as much as possible, even several times on the same day.
[There is a clear preference as seen here for singing, and while prudential allowances are made for instructing and practicing at a manageable pace, and according to the order of importance of the prayers, the ideal is clearly to build up to eventually sing everything.it continues]
28. The distinction between solemn, sung and read Mass, sanctioned by the Instruction of 1958 (n. 3), is retained, according to the traditional liturgical laws at present in force. However, for the sung Mass (Missa cantata), different degrees of participation are put forward here for reasons of pastoral usefulness, so that it may become easier to make the celebration of Mass more beautiful by singing, according to the capabilities of each congregation.
[in order to save space here, please see the document for the degrees listed out, or to make things easy, you may use this link https://www.sfcatholic.org/worship/priority-of-music-at-mass/ to a helpful page put together by the diocese of Souix Falls. This dynamic of gradual teaching to the point of being able to offer God the most we’re capable of and then to grow our capability was already said, including a simplified form of the list, earlier in the document:]
6…those parts especially should be sung which by their very nature require to be sung, using the kind and form of music which is proper to their character. 7…in selecting the parts which are to be sung, one should start with those that are by their nature of greater importance, and especially those which are to be sung by the priest or by the ministers, with the people replying, or those which are to be sung by the priest and people together. The other parts may be gradually added according as they are proper to the people alone or to the choir alone.
16. One cannot find anything more religious and more joyful in sacred celebrations than a whole congregation expressing its faith and devotion in song. Therefore the active participation of the whole people, which is shown in singing, is to be carefully promoted as follows:
(a) It should first of all include acclamations, responses to the greetings of the priest and ministers and to the prayers of litany form, and also antiphons and psalms, refrains or repeated responses, hymns and canticles.[16]
(b) Through suitable instruction and practices, the people should be gradually led to a fuller—indeed, to a complete—participation in those parts of the singing which pertain to them.
(c) …the complete exclusion of the people’s participation in the singing, is to be deprecated.
33. It is desirable that the assembly of the faithful should participate in the songs of the Proper as much as possible, especially through simple responses and other suitable settings.

From the General Instruction of the Roman Missal or GIRM for short
The Importance of Singing
39. The Christian faithful who gather together as one to await the Lord’s coming are instructed by the Apostle Paul to sing together psalms, hymns, and spiritual songs (cf. Col 3:16). Singing is the sign of the heart’s joy (cf. Acts 2:46). Thus St. Augustine says rightly, “Singing is for one who loves.”[48] There is also the ancient proverb: “One who sings well prays twice.”
40. Great importance should therefore be attached to the use of singing in the celebration of the Mass, with due consideration for the culture of the people and abilities of each liturgical assembly. Although it is not always necessary (e.g., in weekday Masses) to sing all the texts that are of themselves meant to be sung, every care should be taken that singing by the ministers and the people is not absent in celebrations that occur on Sundays and on holy days of obligation. [unless we practice sometimes, we won’t be ready or able to sing when it’s most necessary].
In the choosing of the parts actually to be sung, however, preference should be given to those that are of greater importance and especially to those to be sung by the priest or the deacon or the lector, with the people responding, or by the priest and people together.[49]
41. All other things being equal, Gregorian chant holds pride of place because it is proper to the Roman Liturgy. Other types of sacred music, in particular polyphony, are in no way excluded, provided that they correspond to the spirit of the liturgical action and that they foster the participation of all the faithful.[50]
Since faithful from different countries come together ever more frequently, it is fitting that they know how to sing together at least some parts of the Ordinary of the Mass in Latin, especially the Creed and the Lord’s Prayer, set to the simpler melodies.[51]

And lastly, what the Catechism of the Catholic Church has to say
Singing and music
1156 “The musical tradition of the universal Church is a treasure of inestimable value, greater even than that of any other art. the main reason for this pre-eminence is that, as a combination of sacred music and words, it forms a necessary or integral part of solemn liturgy.”20 The composition and singing of inspired psalms, often accompanied by musical instruments, were already closely linked to the liturgical celebrations of the Old Covenant. The Church continues and develops this tradition: “Address . . . one another in psalms and hymns and spiritual songs, singing and making melody to the Lord with all your heart.” “He who sings prays twice.”21
1157 Song and music fulfill their function as signs in a manner all the more significant when they are “more closely connected . . . with the liturgical action,”22 according to three principal criteria: beauty expressive of prayer, the unanimous participation of the assembly at the designated moments, and the solemn character of the celebration. In this way they participate in the purpose of the liturgical words and actions: the glory of God and the sanctification of the faithful:23
How I wept, deeply moved by your hymns, songs, and the voices that echoed through your Church! What emotion I experienced in them! Those sounds flowed into my ears distilling the truth in my heart. A feeling of devotion surged within me, and tears streamed down my face – tears that did me good.24
1158 The harmony of signs (song, music, words, and actions) is all the more expressive and fruitful when expressed in the cultural richness of the People of God who celebrate.25 Hence “religious singing by the faithful is to be intelligently fostered so that in devotions and sacred exercises as well as in liturgical services,” in conformity with the Church’s norms, “the voices of the faithful may be heard.” But “the texts intended to be sung must always be in conformity with Catholic doctrine. Indeed they should be drawn chiefly from the Sacred Scripture and from liturgical sources.”26
Further titles

II. Some things saints and others (perhaps future saints) have to say about singing.
Recent popes
Pope Benedict XVI
“The art of music, [ is ] uniquely called to instill hope in the human spirit, so scarred and sometimes wounded by the earthly condition.” Speech 04.24.08
“It is hard to find words to convey the joy of the soul’s loving encounter with God, yet fine music is able to express something of the mystery of his love for us and ours for him.” Speech 12.30.10
“Music, great music, relaxes the mind, awakens profound sentiments and is, as it were, a natural invitation to raise one’s mind and heart to God in every situation of human existence, both joyful and sad. Music can become prayer.” Speech 10.17.09
“The music is capable of opening minds and hearts to the dimension of the spirit and leads people to lift their gaze to the Most High, to open themselves to the absolute Good and Beauty whose ultimate source is in God.” Speech 04.29.10
“By raising the soul to contemplation, music also helps us grasp the most intimate nuances of human genius, in which is reflected something of the incomparable beauty of the Creator of the universe.” Speech 04.21.06
“As an art music can be a particularly important way of proclaiming Christ because it succeeds in making his mystery perceptible with an eloquence all its own.” Speech 02.12.09
“Singing itself is almost like flying, rising up to God; it is in some way an anticipation of eternity when we will be able to “unceasingly sing God’s praise”.”Speech 10.22.05
“Joyful singing and music is likewise a constant invitation to believers and to all people of good will to work hard to give humanity a future rich in hope.” Speech 04.29.10
“The singing of the Church comes ultimately out of love. It is the utter depth of love that produces the singing. “Cantare amantis est”, says St. Augustine, singing is a lover’s thing. In so saying, we come again to the trinitarian interpretation of Church music. The Holy Spirit is love, and it is he who produces the singing. He is the Spirit of Christ, the Spirit who draws us into love for Christ and so leads to the Father.” -Pope Benedict XVI, “The Spirit of the Liturgy”, (SF, CA: Ignatius, 2000), p. 142.

Venerable Pope Pius XII
“As regards music, let the clear and guiding norms of the Apostolic See be scrupulously observed. Gregorian chant, which the Roman Church considers her own as handed down from antiquity and kept under her close tutelage, is proposed to the faithful as belonging to them also. In certain parts of the liturgy the Church definitely prescribes it;[171] it makes the celebration of the sacred mysteries not only more dignified and solemn but helps very much to increase the faith and devotion of the congregation. For this reason, Our predecessors of immortal memory, Pius X and Pius XI, decree — and We are happy to confirm with Our authority the norms laid down by them — that in seminaries and religious institutes, Gregorian chant be diligently and zealously promoted, and moreover that the old Scholae Cantorum be restored, at least in the principal churches. This has already been done with happy results in not a few places.” -Venerable Pope Pius XII, Mediator Dei #191, November 20, 1947
“St. Paul showed us clearly that sacred chant was used and held in honor from the very beginning in the Church founded by the Divine Redeemer when he wrote to the Ephesians: “Be filled with the Spirit, speaking to one another in psalms and hymns and spiritual songs.”[Eph. 5. 18ff; cf. Col. 3. 16.] He indicates that this custom of singing hymns was in force in the assemblies of Christians when he says: “When you come together each of you has a hymn.”[I Cor. 14. 26.] -Venerable Pope Pius XII, Musicae Sacrae #8, December 25, 1955
“We are not unaware that, for serious reasons, some quite definite exceptions have been conceded by the Apostolic See. We do not want these exceptions extended or propagated more widely, nor do We wish to have them transferred to other places without due permission of the Holy See. Furthermore, even where it is licit to use these exemptions, local Ordinaries and the other pastors should take great care that the faithful from their earliest years should learn at least the easier and more frequently used Gregorian melodies, and should know how to employ them in the sacred liturgical rites, so that in this way also the unity and the universality of the Church may shine forth more powerfully every day.” -Venerable Pope Pius XII, Musicae Sacrae #46, December 25, 1955

“Let the sober banquet resound with Psalms. And if your memory be good and your voice pleasant, approach this work according to custom. You give more nourishment to those dearest to you if we hear spiritual things and if religious sweetness delights the ears.” -Saint Cyprian of Carthage [A.D. 190-258], Letter to Donatus (Letter 1, n. 16) PL, IV, 227.
“Music, that is the science or the sense of proper modulation, is likewise given by God’s generosity to mortals having rational souls in order to lead them to higher things.” -Saint Augustine, Epis. 161. De origine animae hominis, 1, 2; PL XXXIII, 725.
“I feel that our souls are moved to the ardor of piety by the sacred words more piously and powerfully when these words are sung than when they are not sung, and that all the affections of our soul in their variety have modes of their own in song and chant by which they are stirred up by an indescribable and secret sympathy.” -Saint Augustine, Confessions, Book X, chap. 33, MPL, XXXII, 799ff.

Even if you do not understand the meaning of the words, for the time being teach your mouth to say them, for the tongue is sanctified by the words alone whenever it says them with good will.
—St. John Chrysostom, On Psalm 41:2, (PG 55:158)

The soul of one who serves God always swims in joy, always keeps holiday, and is always in the mood for singing. – St. John of the Cross, doctor of the Church

These qualities [sacredness, beauty, universality] are to be found, in the highest degree, in Gregorian Chant, which is, consequently, the Chant proper to the Roman Church, the only chant she has inherited from the ancient fathers, which she has jealously guarded for centuries in her liturgical codices, which she directly proposes to the faithful as her own, which she prescribes exclusively for some parts of the liturgy, and which the most recent studies have so happily restored to their integrity and purity.
On these grounds Gregorian Chant has always been regarded as the supreme model for sacred music, so that it is fully legitimate to lay down the following rule: the more closely a composition for church approaches in its movement, inspiration and savor the Gregorian form, the more sacred and liturgical it becomes; and the more out of harmony it is with that supreme model, the less worthy it is of the temple.
The ancient traditional Gregorian Chant must, therefore, in a large measure be restored to the functions of public worship, and the fact must be accepted by all that an ecclesiastical function loses none of its solemnity when accompanied by this music alone.
Special efforts are to be made to restore the use of the Gregorian Chant by the people, so that the faithful may again take a more active part in the ecclesiastical offices, as was the case in ancient times.
–St Pius X, Tra le sollecitudini paragraph 3

“Among the musical expressions that correspond best with the qualities demanded by the notion of sacred music, especially liturgical music, Gregorian chant has a special place. The Second Vatican Council recognized that ‘being specially suited to the Roman Liturgy'[Sacrosanctum Concilium #116] it should be given, other things being equal, pride of place in liturgical services sung in Latin [Cf. Sacred Congregation for Rites, Instruction on Music in the Sacred Liturgy Musicam Sacram (5 March 1967), 50: AAS 59 (1967), 314.]. St Pius X pointed out that the Church had ‘inherited it from the Fathers of the Church’, that she has ‘jealously guarded [it] for centuries in her liturgical codices’ and still ‘proposes it to the faithful’ as her own, considering it ‘the supreme model of sacred music'[Tra le Sollecitudini #3]. Thus, Gregorian chant continues also today to be an element of unity in the Roman Liturgy.” -Pope Saint John Paul II, Chirograph for the Centenary of Tra le Sollecitudini, the Feast of St Cecilia – 22 November 2003

III. further helpful resources from bishops, parishes, theologians, etc
Once again, bishop Olmstead’s work is excellent

From a parish perspective

This is only the first in a 5 part series doing a deep dive on the history of the past century

From Word on Fire (Bishop Barron’s organization)

From a contemporary theologian

From a common resource for priests, interestingly, this article was written by a guy I went to seminary with. He is very holy, loving and kind as well as brilliant https://www.hprweb.com/2020/10/a-primer-on-liturgical-music/

From Fr. Fessio, founder and chief editor of Ignatius Press, an illustrious, Catholic publisher, e.g. they are solely entrusted with the english translations of all of Pope Benedict XVI’s works

One more theologian and director

Is it any wonder, therefore, that Handel wrote the Messiah and all the best composers were inspired by Scripture and the prayer of the Church, the liturgy? Or why both the worlds of Tolkien (best selling story in history) and Lewis, Middle Earth and Narnia, were written by their authors as sung into being?