"The king shall joy in thy strength, O LORD; and in thy salvation how greatly shall he rejoice!" (Psalm 21:1).
Why would any king need to look higher for anything? The king is the top, the ultimate authority, and the benefactor of his subjects. So why should David turn to the Lord to receive blessings or material goods? The answer is that this king was committed to the King of kings. David was a subject of a higher kingdom than his own.
One attribute of the Lord is His strength--that inherent capacity to act upon or affect something. David suggests that God's strength has provided his salvation; changing his own lost and dying state into a state of eternal life. "He asked life of thee, and thou gavest it him, even length of days for ever and ever" (v. 4). How could David have accomplished that miracle with resources from within his kingdom? Neither his people, his money, nor his authority could provide it.
David had desires in his heart which only God knew and gave him. The Lord gave him "blessings of goodness" (v. 3), "a crown of pure gold on his head" (v. 3), "honor and majesty" (v. 5), and "made him most blessed for ever" (v. 6). No wonder David found joy in the Lord's strength and rejoiced in his saved state. "The king trusteth in the Lord, and through the mercy of the most high he shall not be moved" (v. 7).
How did the Lord accomplish this? Through the agent of His own right hand (v. 8). Work requires a force applied through a distance. The Lord truly has to change our position from lost to saved. There has to be a point of decision in time when we agree with God to change our state. Herein is where His power comes into play (God's force on an object, moving it from lost to saved in a moment of real time).
Let us join with David as he concludes: "Be thou exalted, Lord, in thine own strength: so will we sing and praise thy power" (v. 13). KBC