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.

People's New Testament

19:21 And the remnant were slain with the sword of him that sat upon the horse. This is probably symbolic. If these who had been sinners and supporters of the powers of evil were incapacitated for that support longer, it would be their death (separation) from that cause. It may be that this remnant were converted by the word.

And all the fowls were filled with their flesh. If this is a symbol its signification is that the victory was complete.

Wesley's Notes

19:21 Here is a most magnificent description of the overthrow of the beast and his adherents. It has, in particular, one exquisite beauty; that, after exhibiting the two opposite armies, and all the apparatus for a battle, verse s 11 - 19; Rev 19:11 - 19 then follows immediately, verse 20, 19:20 the account of the victory, without one word of an engagement or fighting. Here is the most exact propriety; for what struggle can there be between omnipotence, and the power of all the creation united against it! Every description must have fallen short of this admirable silence.

Jamieson-Fausset-Brown Bible Commentary

21. the remnant-Greek, "the rest," that is, "the kings and their armies" (Re 19:19) classed together in one indiscriminate mass. A solemn confirmation of the warning in Ps 2:10.

Matthew Henry's Concise Commentary

19:11-21 Christ, the glorious Head of the church, is described as on a white horse, the emblem of justice and holiness. He has many crowns, for he is King of kings, and Lord of lords. He is arrayed in a vesture dipped in his own blood, by which he purchased his power as Mediator; and in the blood of his enemies, over whom he always prevails. His name is The Word of God; a name none fully knows but himself; only this we know, that this Word was God manifest in the flesh; but his perfections cannot be fully understood by any creature. Angels and saints follow, and are like Christ in their armour of purity and righteousness. The threatenings of the written word he is going to execute on his enemies. The ensigns of his authority are his name; asserting his authority and power, warning the most powerful princes to submit, or they must fall before him. The powers of earth and hell make their utmost effort. These verses declare important events, foretold by the prophets. These persons were not excused because they did what their leaders bade them. How vain will be the plea of many sinners at the great day! We followed our guides; we did as we saw others do! God has given a rule to walk by, in his word; neither the example of the most, nor of the chief, must influence us contrary thereto: if we do as the most do, we must go where the most go, even into the burning lake.