Psalms 21:1
1The king rejoices in your strength, LORD! How greatly he rejoices in your salvation!
Wesley frames the psalm as thanksgiving answering Psalm 20’s prayers—praises for blessings received concerning the king, with David looking beyond himself to Christ.
Joy is in the LORD’s strength and salvation, not in the king’s self-made triumph. The anointed exults because God has saved; the congregation learns to rejoice where strength truly sits. Grace enables that rejoicing; the people still must ascribe salvation to the LORD and refuse to steal the song for themselves.
Calvin: David could have thanked God privately, but intends to testify that God elevated him and that blessings on him redound to the public good. Believing Israelites express persuasion that God, who created David king, has undertaken to defend him. Strength and salvation mean strong succor—God’s power preserving the king against all dangers.
The king rejoices in God’s strength, not his own. The king’s face is a mirror of God’s reconciled countenance; safety of the head is safety of the body under the Head God appointed.