Book 4 of Psalms (Psalms 90-106) explores themes of human suffering, God's greatness in creation, His faithfulness throughout history, and the contrast between God's goodness and Israel's unfaithfulness. Key psalms include 102, a prayer of an afflicted person, 103, a call to praise for God's forgiveness, and 104, which celebrates creation while linking it to Jesus. The section serves as a transition toward the promised land in Book 5, emphasizing God's mercy amid human disobedience.