The king shall joy in thy strength, O LORD; and in thy salvation how greatly shall he rejoice!
This 21st forms a pair with the 20th Psalm. The blessings there prayed for "in the day of trouble" are here triumphantly acknowledged as already granted. These bright anticipations are based on God's promise to David (2 Samuel 7:16; 2 Samuel 7:24-29; 2 Samuel 23:5-7) that his house and throne should be forever: fulfilled in the Son of David (Psalms 72:5; Psalms 72:15; Psalms 72:17). Psalms 21:1-13.-Yahweh's strength bringing salvation, at the King's desire, is praised (Psalms 21:1-2); the king's crown, glory, and everlasting life derived through trust in Yahweh (Psalms 21:3-7); address to the king, anticipating his triumph (Psalms 21:8-12); closing prayer to God to exalt Himself in His own strength, so as to give His people cause for praise (Psalms 21:13).
In thy strength, O Lord, and in thy salvation. It shall be the element IN which his joy shall have place. "Salvation" means here, in its reference to David primarily, and mainly to Messiah, deliverance from all enemies and final triumph (cf. "thy salvation," Psalms 21:5).