Some quotes related to psalm-singing, compiled by Brad Kelly:
Athanasius (c.296-373) bishop of Alexandria:
They appear to me a mirror of the soul of every one who sings them; they enable him to perceive his own emotions, and to express them in the words of the Psalms. He who hears them read receives them as if they were spoken for him. Conscience-struck, he will either humbly repent, or hearing how the trust of believers was rewarded by God, rejoice as if His mercy were promised to him in particular, and begin to thank God. Yet, in its pages you find portrayed man’s whole life, the emotion of his soul, and the frames of his mind. We cannot conceive of anything richer than the Book of Psalms. If you need penitence, if anguish or temptation have befallen you, if you have escaped persecution and oppression, or are immersed in deep affliction, concerning each and all you may find instruction, and state it to God in the words of the Psalter!
John Chrysostom (c.347-407) bishop of Constantinople:
All Christians employ themselves in David’s Psalms more frequently than in any other part of the Old or New Testament. The grace of the Holy Ghost hath so ordered it that they should be recited and sung every night and day. In the church’s vigils, the first, the midst, and the last are David’s Psalms. In the morning David’s Psalms are sought for; and David is the first, the midst, and the last. At funeral solemnities, the first, the midst, and the last is David. Many who know not a letter can say David’s Psalms by heart. In private houses where virgins spin—in the monasteries—in the deserts, where men converse with God—the first, the midst, and the last is David. In the night, when men are asleep, he wakes them up to sing; and collecting the servants of God into angelic troops, turns earth into heaven, and of men makes angels, chanting David’s Psalms. (Homily 6, On Penitence).
Augustine (354-430) bishop of Hippo:
Oh! In what accents spake I unto Thee, my God, when I read the Psalms of David, those faithful songs and sounds of devotion, which allow of no swelling spirit! Oh! What accents did I utter unto Thee in those psalms! And how was I by them kindled toward Thee, and on fire to rehearse them if possible, through the whole world, against the pride of mankind! And yet they are sung through the whole world, nor can any hide himself from Thy heat.
Hence it is that the Psalter is the book of all saints; and everyone, in whatever situation he might be, finds in that situation psalms and words that fit his case, that suit him as if they were put there just for his sake, so that he could not put it better himself, or find or find or wish for anything better. (Luther’s Works, vol. 35: Word and Sacrament I; quoted in Patrick D. Miller, Interpreting the Psalms 19-20)
James L. Mays:
Periods and eras, with their fashions and styles as well as sensibilities, came and passed away. The psalms were the constant, the continuity, the common language across the ages. Along with Scripture and the catholic creeds, they are a foundational component of community in the world church. (James L. Mays, The Lord Reigns, 5)