The book of Psalms is split up into 5 separate books, but Psalms 1-2 is separated from the first book as an introduction. These two Psalms are setting the stage for the rest of the Psalms. The first one is about how those who meditate “day and night” on the instructions of God are blessed and will prosper, like trees planted along streams of water. The second Psalm alludes to God’s messianic King, and it’s kind of vague, but it leaves readers anticipating a new kind of King that they’ve never seen before. This introduction sets up the Psalms as a book of poetic prayers for those who want to meditate on God’s instruction and His messianic King.