Albert Barnes Commentary Psalms 21:13

"Be thou exalted, O Jehovah, in thy strength: So will we sing and praise thy power." — Psalms 21:13 (ASV)

Be thou exalted, Lord, in thine own strength - This is the concluding part of the psalm (see the introduction), expressing a desire that God “might” be exalted over all His foes, or that His own strength might be so manifestly put forth that He would be exalted as He ought to be. This is the ultimate and chief desire of all holy created beings, that God might be exalted in the estimation of the universe above all other beings—or that He might so triumph over all His enemies as to reign supreme.

So will we sing and praise thy power - That is, as the result of Your being thus exalted to proper honor, we will unite in celebrating Your glory and Your power. Compare Revelation 7:10-12; Revelation 12:10; Revelation 19:1–3. This will be the result of all the triumphs which God will achieve in the world, that the holy beings of all worlds will gather around His throne and “sing and praise His power.” The “thought” in the psalm is that God will ultimately triumph over all His foes, and that this triumph will be followed by universal rejoicing and praise. Come that blessed day!