33 St. Augustine, speaking of chants characterized by "beautiful voice and most apt melody," says: "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."
Source: Musicae Sacrae (Vatican.va)