The Psalms, ah!
147. The Psalms, as all know, form the chief part of the divine office. They encompass the full round of the day and sanctify it. Cassiodorus speaks beautifully about the Psalms as distributed in his day throughout the divine office: “With the celebration of matins they bring a blessing on the coming day, they set aside for us the first hour and consecrate the third hour of the day, they gladden the sixth hour with the breaking of bread, at the ninth they terminate our fast, they bring the evening to a close and at nightfall they shield our minds from darkness.”[Explicatio in Psalterium, Preface. Text as found in Migne, Parres Larini, 70:10. But some are of the opinion that part of this passage should not be attributed to Cassiodorus.]
The quote attributed to Cassiodorus is fine. I especially like the image of psalmody as a shield against the darkness.
Psalms are amazingly diverse, not only in genre, but also in the expression of the human relationship with God:
148. The Psalms recall to mind the truths revealed by God to the chosen people, which were at one time frightening and at another filled with wonderful tenderness; they keep repeating and fostering the hope of the promised Liberator which in ancient times was kept alive with song, either around the hearth or in the stately temple; they show forth in splendid light the prophesied glory of Jesus Christ: first, His supreme and eternal power, then His lowly coming to this terrestrial exile, His kingly dignity and priestly power and, finally, His beneficent labors, and the shedding of His blood for our redemption. In a similar way they express the joy, the bitterness, the hope and fear of our hearts and our desire of loving God and hoping in Him alone, and our mystic ascent to divine tabernacles.
Saint Ambrose on the psalms:
149. “The psalm is . . . a blessing for the people, it is the praise of God, the tribute of the nation, the common language and acclamation of all, it is the voice of the Church, the harmonious confession of faith, signifying deep attachment to authority; it is the joy of freedom, the expression of happiness, an echo of bliss.”[Saint Ambrose, Enarr in Ps. 1, n. 9]