The Jewish Psalter became the first hymn-book of the Church, and still remains the backbone of its ordered daily worship: the reading and expounding of the Old Testament, stressing the historical character of the Christian revelation, as from the beginning a vital part of the ministry of the Word. Thus Christian worship, though from one point of view it was indeed a “new song”, from another accepts and completes the devotion of the synagogue, and shows forth in its fullness the spiritual mystery towards which the sacrifices of the Temple looked. Here as elsewhere the revelation of God, breaking in upon history, accepts and clothes itself in historical forms
—Evelyn Underhill. Worship. P. 194. (HT "Sublunary Sublime")
Any reader of the Confessions will be aware that, for Augustine, the reading of the Psalms was more than simply a “devotional” reading of a holy text, let alone reading to inform or instruct. The psalmist’s voice is what releases two fundamentally significant things for the Augustinian believer. It unseals deep places, emotions otherwise buried, and it provides an analogy for the unity or intelligibility of a human life lived in faith. Here is a conversation with God that has a beginning, a middle, and an end. And in the course of that conversation, the human speaker is radically changed and enabled to express what is otherwise hidden from him or her. Augustine speaks of what the psalm he is discussing (Psalm 4, Cum invocarem) “makes of him”: the act of recitation becomes an opening to the transforming action of grace (Conf. 9.4.8).
—Rowan Williams. “Augustine and the Psalms.” Interpretation 58, no. 1 (January 2004) (HT winged keel and crumpet)