What does Psalm 21:8 mean?

The congregation expresses confidence in David's military success. He will find out his enemies and those who hate him. "Find out," in this context, includes the idea of "disposing of" something. No enemy will be able to withstand David's power.

The right hand is a term used in Scripture to signify power or strength. There may be a messianic implication here, as well. Jesus, the Messiah, the Son of David, will dispose of all His enemies, those who hate Him. When He returns to earth, singlehandedly He will dispose of those who support the beast and the false prophet. He will overwhelmingly defeat these evil leaders, who dupe millions of people in the tribulation: the seven-year period that follows the rapture.

Jude 1:14–15 promises that Jesus will return "with ten thousands of his holy ones, to execute judgment on all and to convict all the ungodly of all their deeds of ungodliness that they have committed in such an ungodly way, and of all the harsh things that ungodly sinners have spoken against him." Revelation 19:15–21 pictures the return of Jesus as He strikes down the nations and throws the beast and the false prophet into the lake of fire.