Psalm 21--The king shall joy in thy strength, O LORD; and in thy salvation how greatly shall he rejoice! Thou hast given him his heart's desire, and hast not withholden the request of his lips. Selah. For thou preventest him with the blessings of goodness: thou settest a crown of pure gold on his head. He asked life of thee, and thou gavest it him, even length of days for ever and ever. His glory is great in thy salvation: honour and majesty hast thou laid upon him. For thou hast made him most blessed for ever: thou hast made him exceeding glad with thy countenance. For the king trusteth in the LORD, and through the mercy of the most High he shall not be moved. Thine hand shall find out all thine enemies: thy right hand shall find out those that hate thee. Thou shalt make them as a fiery oven in the time of thine anger: the LORD shall swallow them up in his wrath, and the fire shall devour them. Their fruit shalt thou destroy from the earth, and their seed from among the children of men. For they intended evil against thee: they imagined a mischievous device, which they are not able to perform. Therefore shalt thou make them turn their back, when thou shalt make ready thine arrows upon thy strings against the face of them. Be thou exalted, LORD, in thine own strength: so will we sing and praise thy power.

This king spoken of here is Christ. Christ rejoices in the strength of His Father's saving power for His people. God has given Christ His heart's desire. What is Christ's desire? That God will keep through His own Name those whom He has chosen.

As far as Christ's exaltation goes, it says that God bestows on Him blessings of goodness, and a golden crown on his head. God adorns Christ with honor and majesty. Through God's power, the exalted Christ is made exceeding glad, and shall never be moved. Rather, Christ's enemies are moved, and scattered in desolation. Because God is Sovereign, the enemy can't perform the evil that they imagine against Christ. They are turned backward, and the righteous sing for joy. They sing praises to the exalted Lord.