The unique element in the book of Psalms is that it allows the reader to get inside the personalities and events of the Old Testament as a participant; or, perhaps better said, it allows these personalities and events to get inside the reader as an emotive factor in shaping his or her life in accordance with the teachings found there. “In addition to the other matters in which the book of Psalms is related to the other books,” Athanasius says, “it also possesses the unique and marvelous feature that the emotions of each soul have been recorded there. The changes and corrections of these emotions are described and portrayed in the book. Consequently, someone who desires to receive and learn from it without limit, as it were, shapes himself in this way” (Letter to Marcellinus 10). What Athanasius means, as he proceeds to explain, is that in the book of Psalms we are not only told what we should do, as we are in the law, for example, but we are actually helped to do it. We are not only instructed to repent, we are also given the emotions and the words of repentance. We are not only told we should praise or petition God, we are also led into the emotions of praise and petition and given the words to use in expressing them (Letter to Marcellinus 10).
Quoted from Ronald E. Heine, Reading the Old Testament with the Ancient Church: Exploring the Formation of Early Christian Thought (Grand Rapids: Baker Academic, 2007), 149.