I came across this section of a speech Pope Benedict made on September 12, 2008 at the Collège des Bernardins in Paris.
"For prayer that issues from the word of God, speech is not enough: music is required. Two chants from the Christian liturgy come from biblical texts in which they are placed on the lips of angels: the ‘Gloria,’ which is sung by the angels at the birth of Jesus, and the ‘Sanctus,’ which according to Isaiah 6 is the cry of the seraphim who stand directly before God. Christian worship is therefore an invitation to sing with the angels, and thus to lead the word to its highest destination.[...] From this perspective one can understand the seriousness of a remark by Saint Bernard of Clairvaux, who used an expression from the Platonic tradition handed down by Augustine, to pass judgement on the poor singing of monks, which for him was evidently very far from being a mishap of only minor importance. He describes the confusion resulting from a poorly executed chant as a falling into the ‘regio dissimilitudinis,’ the ‘zone of dissimilarity’ [...], into a remoteness from God, in which man no longer reflects Him, and so has become dissimilar not only to God, but to himself, to what being human truly is. Bernard is certainly putting it strongly when he uses this phrase, which indicates man’s falling away from himself, to describe bad singing by monks. But it shows how seriously he viewed the matter. It shows that the culture of singing is also the culture of being, and that the monks have to pray and sing in a manner commensurate with the grandeur of the word handed down to them, with its claim on true beauty. This intrinsic requirement of speaking with God and singing of Him with words He Himself has given, [texts of Sacred Scripture] is what gave rise to the great tradition of Western music. It was not a form of private ‘creativity’, in which the individual leaves a memorial to himself and makes self-representation his essential criterion. Rather it is about vigilantly recognizing with the ‘ears of the heart’ the inner laws of the music of creation, the archetypes of music that the Creator built into his world and into men, and thus discovering music that is worthy of God, and at the same time truly worthy of man, music whose worthiness resounds in purity.”
It is an internal quotation from an article discussed by Fr John Zuhlsdorf, which notes, alas, that the Holy Father has not, so far, done much in the musical field as Pope, despite his evident interest in the matter and the powerful things he has said about it.