The book of Psalms is a collection of song lyrics. Like many songs, they were first written in response to events in the lives of their authors. Later, the whole community used them in worship. When Israel returned from exile in Babylon many of the songs from over the centuries were collected in the book of Psalms.
The book is structured into five parts marked off by the phrase, Praise be to the Lord… Amen and Amen! These five “books” remind the reader of the five books of Moses. Like the law, these song lyrics can be read and studied for instruction. Psalm 1 emphasizes such meditation and seems to have been placed first to make this point.
The five books also tell a three-part story of Israel’s redemption: monarchy, exile and return. The psalms of King David dominate books one and two. The beginning and ending of book three highlight Israel’s exile. The fourth book ends with a plea that God bring the exiled people home. The fifth book declares that God has done just that. Now the reason for the group of praise psalms at the end of the book is apparent: God has been faithful, judging Israel in exile but then bringing the nation home again.
The book of Psalms thus operates at two levels: individually the songs explore a wide variety of honest spiritual responses to God, while the overall collection tells, and celebrates, the work of God in history to save his people.