Psalms 21:1

The king shall joy in thy strength, O LORD; and in thy salvation how greatly shall he rejoice!

The Hebrew wording allows the line to be read as a king rejoicing in divine strength and deliverance, and the context supports supplying the indefinite article rather than requiring a definite sense. The two parallel clauses express the same thought in different words, underscoring the king's joy in God's delivering power. The psalm belongs with those that teach trust and confidence in God, locating the king's joy and boasting in the Lord's strength and in the greatness of his rejoicing in His salvation.

That rejoicing also makes God's saving work known abroad. It defines what the anointing of Christ with the oil of gladness above His fellows means, for the King anointed by God rejoices in the Lord's strength and rejoices greatly in His salvation, is made most blessed forever, and is made exceeding glad with God's countenance. Fellows there means companions or associates and does not imply equality.

Verses 1 through 7 foretell how the Father heard Jesus when in the days of His mortal life He offered prayers and supplications with strong crying and tears in agony in Gethsemane to Him who was able to save Him from death, heard because of godly fear. That hearing was salvation and life given to the king who joys in the Lord's strength and rejoices greatly in His salvation, fulfilling the confidence He had expressed in Psalm 16:8-11 that the Father would give Him life. The Father answered by raising Christ from the dead to die no more, with death having no more dominion over Him. The earth and everyone in it belong to God by creation and by redemption through Christ, who gave Himself to reclaim what humanity had surrendered to sin, and His ownership extends to every part of life including each person's heart and body, so that peace with God requires acknowledging His authority and yielding to Him.