From the Explanations of the Psalms by Saint Ambrose –The appeal of the Book of Psalms
Though all Scripture is fragrant with God’s grace, the Book of Psalms has a special attractiveness.
Moses wrote the history of Israel’s forefathers in prose, but after leading the people through the Red Sea–a wonder that remained in their memory–he broke into a song of triumph in praise of God when he saw King Pharaoh drowned along with his forces. His genius soared to a higher level, to match an accomplishment beyond his own powers.
Miriam too raised her timbrel and sang encouragement for the rest of the women, saying: Let us sing to the Lord, for he has triumphed gloriously; he has cast horse and rider into the sea.
In the Book of Psalms there is profit for all, with healing power for our salvation. There is instruction from history, teaching from the law, prediction from prophecy, chastisement from denunciation, persuasion from moral preaching. All who read it may find the cure for their own individual failings. All with eyes to see can discover in it a complete gymnasium for the soul, a stadium for all the virtues, equipped for every kind of exercise; it is for each to choose the kind he judges best to help him gain the prize.
If you wish to read and imitate the deeds of the past, you will find the whole history of the Israelites in a single psalm: in one short reading you can amass a treasure for the memory. If you want to study the power of the law, which is summed up in the bond of charity (Whoever loves his neighbor has fulfilled the law), you may read in the psalms of the great love with which one man faced serious dangers singlehandedly in order to remove the shame of the whole people. You will find the glory of charity more than a match for the parade of power.
What am I to say of the grace of prophecy? We see that what others hinted at in riddles was promised openly and clearly to the psalmist alone: the Lord Jesus was to be born of his seed, according to the word of the Lord, I will place upon your throne one who is the fruit of your flesh.
In the psalms, then, not only is Jesus born for us, he also undergoes his saving passion in his body, he lies in death, he rises again, he ascends into heaven, he sits at the right hand of the Father. What no man would have dared to say was foretold by the psalmist alone, and afterward proclaimed by the Lord himself in the Gospel.