The superscription of this Psalm claims that it was written by Ethan, the Ezrahite. Ethan the Ezrahite, along with Heman the Ezrahite (the author of the preceding Psalm, Psalm 88), was a wise man from the time of Solomon. 1 Kings 4:31 states, concerning King Solomon, "For he was wiser than all other men, wiser than Ethan the Ezrahite, and Heman, Calcol, and Darda, the sons of Mahol, and his fame was in all the surrounding nations" (ESV).
Psalm 89 begins with words of praise for Yahweh's goodness and covenant faithfulness. It recounts the promises made to King David, and the covenant which God had established with him, for the first 37 verses; from verse 38 to 51, the Psalmist laments what seemed like God's lack of remembrance of his covenant promises. But finally, in the 52nd and closing verse of the Psalm, the Psalmist's tone changes once again, when he proclaims, "Blessed be the LORD forever! Amen and Amen" (ESV). With these words, the third book of the Psalter is closed.