Revelation 19:21
And the remnant were slain with the sword of him that sat upon the horse, which sword proceeded out of his mouth: and all the fowls were filled with their flesh. And the remnant were slain with the sword of him that sat upon the horse, which sword proceeded out of his mouth: and all the fowls were filled with their flesh.
The rider on the horse is Jesus Christ, marked by the name KING OF KINGS, AND LORD OF LORDS upon His vesture and upon His thigh, leading the armies of heaven on white horses clothed in fine linen, clean and white. The remnant slain are the remaining wicked forces, the armies of the beast and the kings of the earth and the rebellious powers gathered to fight Christ and His army. They are killed by the sharp sword proceeding from His mouth, and the fowls of heaven are filled with their flesh.
This slaughter comes after the beast and the false prophet are seized and cast alive into the lake of fire burning with brimstone. It comes before the dragon is bound for a thousand years and before the later resurrection of the wicked and the final destruction of Satan and all the wicked. Their end comes when Christ returns in glory, and in this way Satan's rebellion is brought to a close. The chapter belongs to the promised final conflict, and its portrayal of last-day calamity and distress is certain and soon to be fulfilled as the closing slaughter of the battle of Armageddon, which is soon to be fought.
The verse belongs to the testing truths of Revelation 18 and 19 that all must read and understand as part of the last call of mercy to be given more fully to the world. God holds back His approaching judgments until the warning message has been sounded to all because many have not yet heard. God uses this destruction to avenge His children who were falsely accused, fettered, imprisoned, and burned for obeying Him. Those who acted in Satan's spirit to inflict pain and who did all in their power to force others to break the law God commanded all to obey will suffer as they made others suffer and will perish by the sword proceeding from Christ's mouth. The judgment assures Christians that God will not overlook or forget the persecutions they suffered at the hands of apostate powers opposing Christ and His army, especially attempts to compel people to do evil through enforced worship.