On Sacred Music...

"Let the sober banquet resound with Psalms. And if your memory by 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.

"They [Bishops] shall also banish from churches all those kinds of music, in which, whether by the organ, or in the singing, there is mixed up any thing lascivious or impure; as also all secular actions; vain and therefore profane conversations, all walking about, noise, and clamour, that so the house of God may be seen to be, and may be called, truly a house of prayer."
-Pope Pius IV, The Council of Trent, Sesion XXII, Sptember 17th, 1562

"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 suprememodel for sacred music, so that it is fully legitimate to lay down thefollowing 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."
-Pope Saint Pius X, Tra le Sollecitudini, November 22, 1903

"Although the music proper to the Church is purely vocal music, music with the accompaniment of the organ is also permitted. In some special cases, within due limits and with proper safeguards, other instruments may be allowed, but never without the special permission of the Ordinary, according to prescriptions of the Caeremoniale Episcoporum. As the singing should always have the principal place, the organ or other instruments should merely sustain and never oppress it. It is not permitted to have the chant preceded by long preludes or to interrupt it with intermezzo pieces. The sound of the organ as an accompaniment to the chant in preludes, interludes, and the like must be not only governed by the special nature of the instrument, but must participate in all the qualities proper to sacred music as above enumerated. The employment of the piano is forbidden in church, as is also that of noisy or frivolous instruments such as drums, cymbals, bells and the like. It is strictly forbidden to have bands play in church, and only in special cases with the consent of the Ordinary will it be permissible to admit wind instruments, limited in number, judiciously used, and proportioned to the size of the placeprovided the composition and accompaniment be written in grave and suitable style, and conform in all respects to that proper to the organ. In processions outside the church the Ordinary may give permission for a band, provided no profane pieces be executed. It would be desirable in such cases that the band confine itself to accompanying some spiritual canticle sung in Latin or in the vernacular by the singers and the pious associations which take part in the procession.
-Pope Saint Pius X, Tra le Sollecitudini, November 22, 1903

"To this lofty dignity of the Church's prayer, there should correspond earnest devotion in our souls. For when in prayer the voice repeats those hymns written under the inspiration of the Holy Ghost and extols God's infinite perfections, it is necessary that the interior sentiment of our souls should accompany the voice so as to make those sentiments our own in which we are elevated to heaven, adoring and giving due praise and thanks to the Blessed Trinity; "so let us chant in choir that mind and voice may accord together."[140] It is not merely a question of recitation or of singing which, however perfect according to norms of music and the sacred rites, only reaches the ear, but it is especially a question of the ascent of the mind and heart to God so that, united with Christ, we may completely dedicate ourselves and all our actions to Him."
-Venerable Pope Pius XII, Mediator Dei #145, November 20, 1947

"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

"The choral chant began to be called "Gregorian" after St. Gregory, the man who revived it. It attained new beauty in almost all parts of Christian Europe after the 8th or 9th century because of its accompaniment by a new musical instrument called the "organ." Little by little, beginning in the 9th century, polyphonic singing was added to this choral chant. The study and use of polyphonic singing were developed more and more during the centuries that followed and were raised to a marvelous perfection under the guidance of magnificent composers during the 15th and 16th centuries."
-Venerable Pope Pius XII, Musicae Sacrae #14, December 25, 1955

"Thus, with the favor and under the auspices of the Church the study of sacred music has gone a long way over the course of the centuries. In this journey, although sometimes slowly and laboriously, it has gradually progressed from the simple and ingenuous Gregorian modes to great and magnificent works of art. To these works not only the human voice, but also the organ and other musical instruments, add dignity, majesty and a prodigious richness."
-Venerable Pope Pius XII, Musicae Sacrae #16, December 25, 1955

"It must be holy. It must not allow within itself anything that savors of the profane nor allow any such thing to slip into the melodies in which it is expressed. The Gregorian chant which has been used in the Church over the course of so many centuries, and which may be called, as it were, its patrimony, is gloriously outstanding for this holiness."
-Venerable Pope Pius XII, Musicae Sacrae #42, 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

"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."
-The Second Vatican Council, Sacrosanctum Concilium #116, December 4th, 1963

"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.

" 'Rock' . . . is the expression of elemental passions, and at rock festivals it assumes a cultic character, a form of worship, in fact, in opposition to Christian worship. People are, so to speak, released from themselves by the experience of being part of a crowd and by the emotional shock of rhythm, noise, and special lighting effects. However, in the ecstasy of having all their defenses torn down, the participants sink, as it were, beneath the elemental force of the universe."
-Pope Benedict XVI, "The Spirit of the Liturgy", (SF, CA: Ignatius, 2000)