Psalm 89
A long celebration of God's covenant with David, sworn by God's holiness, forever, even if David's sons sin (verses 30-37). Then the psalm turns: "Now, however, You have spurned and rejected him." The king has fallen, and the promise seems broken. "Where... is Your loving devotion of old?" Book Three ends with that question still open. The New Testament answers it in Jesus, the Son of David whose throne doesn't end (Luke 1:32-33), but the psalm itself waits honestly.
"But I will not withdraw My loving devotion from him, nor ever betray My faithfulness." (Psalm 89:33)