Book IV is comprised of Psalms 90 through 106. Many of these psalms may be seen as answering the anguished cry of Psa. 89:49, which asks God what became of his faithful promises to David. In Jerusalem’s fall and the death or exile of its royal family members, the Davidic covenant had apparently come to nothing. Thus, Book IV redirects our attention from the failed Davidic monarchy and covenant to YHWH’s kingship and the Mosaic covenant. It refers to Moses a total of 7 times and to Aaron multiple times as well, in order to take the reader back to Israel’s beginning. God was Israel’s refuge long before David became king and continues to protect Israel though the monarchy is gone. It also proclaims the blessedness of all who trust in God.
Book IV is dominated by its enthronement psalms (Psa. 93, 96, 97, 98, 99, and Psa. 94 implicitly) likely used in an annual festival celebrating God’s rule over the nations after the Israelites’ return from exile. Like Book IV as a whole, these psalms respond to Psa. 89 by calling God’s people back to their first commitment, of serving God alone as king. Interestingly, the New Testament has it both ways since Jesus reigns as both David’s greater son and God incarnate.