And, among all the books, the Psalter has certainly a very special grace, a choiceness of quality well worthy to be pondered; for, besides the characteristics which it shares with others, it has this peculiar marvel of its own, that within it are represented and portrayed in all their great variety the movements of the human soul. It is like a picture, in which you see yourself portrayed, and seeing, may understand and consequently form yourself upon the pattern given. Elsewhere in the Bible you read only that the Law commands this or that to be done, you listen to the Prophets to learn about the Saviour's coming, or you turn to the historical books to learn the doings of the kings and holy men; but in the Psalter, besides all these things, you learn about yourself. You find depicted in it all the movements of your soul, all its changes, its ups and downs, its failures and recoveries. Moreover, whatever your particular need or trouble, from this same book you can select a form of words to fit it, so that you do not merely hear and then pass on, but learn the way to remedy your ill. Prohibitions of evil-doing are plentiful in Scripture, but only the Psalter tells you how to obey these orders and abstain from sin....In fact, under all the circumstances of life, we shall find that these divine songs suit ourselves and meet our own souls' need at every turn.
From Athanasius's Letter to Marcellinus. I had never read it before, but I became curious about it while reading this paper (PDF) by Holly Taylor Coolman, which discusses it. The whole letter bears close reading.