Revelation 19:21; And the Remnant
Revelation 19:21 (KJV) 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.
In contrast to the beast and false prophet, the kings of the earth and their armies will lose their lives in this battle – 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 remnant” includes the defeated forces of the beast. These were composed of men, not demons. They have received ample opportunity to repent, but refused. But by extension, it must include all the inhabitants of the earth who do not choose loyalty to the Lamb, but have demonstrated allegiance to the beast instead. The broad coverage of the expression is necessary in light of the exhaustive specification of different groups in Revelation 19:18.
Revelation 19:18 (KJV) That ye may eat the flesh of kings, and the flesh of captains, and the flesh of mighty men, and the flesh of horses, and of them that sit on them, and the flesh of all men, both free and bond, both small and great.
The passive verb “were slain” tells of the fate of this vast portion of living humanity. The text speaks of widespread bloodshed, not of people turning to Christ (Mounce). This is a judgment scene that entails the deaths of the rebels, not their conversion.
This must be a military confrontation. No other understanding will satisfy the meaning of “slain” Just as the beast ‘s warfare against the saints resulted in the loss of life (Revelation 11:7; 13:7; 15), so will the warfare of the rider against the forces of the beast.
Revelation 11:17 (KJV) Saying, We give thee thanks, O Lord God Almighty, which art, and wast, and art to come; because thou hast taken to thee thy great power, and hast reigned.
Revelation 13:7 (KJV) And it was given unto him to make war with the saints, and to overcome them: and power was given him over all kindreds, and tongues, and nations.
Revelation 13:15 (KJV) And he had power to give life unto the image of the beast, that the image of the beast should both speak, and cause that as many as would not worship the image of the beast should be killed.
[Robert L. Thomas, Revelation 8-22 – An Exegetical Commentary, Moody, 1995, 400]