"When, indeed, the Holy Spirit saw that the human race was guided only with difficulty toward virtue, and that, because of our inclination toward pleasure, we were neglectful of an upright life, what did He do? The delight of melody He mingled with the doctrines so that by the pleasantness and softness of the sound heard we might receive without perceiving it the benefit of the words, just as wise physicians who, when giving the fastidious rather bitter drugs to drink, frequently smear the cup with honey. Therefore, He devised for us these harmonious melodies of the Psalms, that they who are children in age or, even those who are youthful in disposition might to all appearances chant but, in reality, become trained in soul. For, never has anyone of the many indifferent persons gone away easily holding in mind either an apostolic or prophetic message, but they do chant the words of the Psalms, even in the home, and they spread them around in the market place, and, if perchance, someone becomes exceedingly wrathful, when he begins to be soothed by the Psalm, he departs with the wrath of his soul immediately lulled to sleep by means of the melody.
"A Psalm implies serenity of soul; it is the author of peace, which calms bewildering and seething thoughts. For, it softens the wrath of the soul, and what is unbridled it chastens. A Psalm forms friendships, unites those separated, conciliates those at enmity. Who, indeed, can still consider as an enemy him with whom he has uttered the same prayer to God? So that psalmody, bringing about choral singing, a bond, as it were, toward unity, and joining the people into a harmonious union of one choir, produces also the greatest of blessings, charity. A Psalm is a city of refuge from the demons; a means of inducing help from the angels, a weapon in fears by night, a rest from toils by day, a safeguard for infants, an adornment for those at the height of their vigor, a consolation for the elders, a most fitting ornament for women. It peoples the solitudes; it rids the market place of excesses; it is the elementary exposition of beginners, the improvement of those advancing, the solid support of the perfect, the voice of the Church. It brightens the feast days; it creates a sorrow which is in accordance with God. For, a Psalm calls forth a tear even from a heart of stone. A Psalm is the work of angels, a heavenly institution, the spiritual incense.
"Oh! the wise invention of the teacher who contrived that while we were singing we should at the same time learn something useful; by this means, too, the teachings are in a certain way impressed more deeply on our minds. Even a forceful lesson does not always endure, but what enters the mind with joy and pleasure somehow becomes more firmly impressed upon it. What, in fact, can you not learn from the Psalms? Can you not learn the grandeur of courage? The exactness of justice? The nobility of self-control? The perfection of prudence? A manner of penance? The measure of patience? And whatever other good things you might mention? Therein is perfect theology, a prediction of the coming of Christ in the flesh, a threat of judgment, a hope of resurrection, a fear of punishment, promises of glory, an unveiling of mysteries; all things, as if in some great public treasury, are stored up in the Book of Psalms."