Psalm 21 feels like the song after the prayer has been answered.
Psalm 20 asks the Lord to help, protect, and save. Psalm 21 turns around and rejoices in the strength and salvation God has given.
“O Lord, in your strength the king rejoices, and in your salvation how greatly he exults!”
This song follows that movement of gratitude, victory, blessing, and praise. The joy of the king is not rooted in his own power, but in the Lord who gives salvation, steadfast love, and strength.
“Be exalted, O Lord, in your strength! We will sing and praise your power.”