"Be exalted, O LORD, in Your strength; We will sing and praise Your power."
Psalm 21 is David's song of praise for what God has done: He has delivered his people from the hands of their enemy. And David looks forward to what God will do in the future. He will continue to rescue His beloved children from their enemies. We have a spiritual enemy -- Satan -- who seeks to destroy us. But he has no power over those who have placed their trust in Jesus Christ. "God makes sinners willing by His grace, receives them to His favour, and delivers them from the wrath to come. May He exalt himself, by His all-powerful grace, in our hearts, destroying all the strong-holds of sin and Satan. How great should be our joy and praise to behold our Brother and Friend upon the throne, and for all the blessings we may expect from Him! Yet He delights in His exalted state, as enabling Him to confer happiness and glory on poor sinners, who are taught to love and trust in Him." -- Matthew Henry.