Albert Barnes Commentary Revelation 19:20

"And the beast was taken, and with him the false prophet that wrought the signs in his sight, wherewith he deceived them that had received the mark of the beast and them that worshipped his image: they two were cast alive into the lake of fire that burneth with brimstone:" — Revelation 19:20 (ASV)

And the beast was taken. That is, was taken alive, to be thrown into the lake of fire. The armies were slain (Revelation 19:21), but the leaders were made prisoners of war. The general idea is that these armies were overcome and that the Messiah was victorious. However, there is an appropriateness in the representation here that the leaders—the authors of the war—should be taken captive and reserved for severer punishment than death on the battlefield would be, for they had stirred up their armies and summoned them to make rebellion against the Messiah.

The beast here, as all along, refers to the Papal power. The idea is that of its complete and utter overthrow, as if the leader of an army were taken captive and tormented in burning flames, and all his followers were cut down on the field of battle.

And with him the false prophet. As they had been practically associated together, there was an appropriateness that they should share the same fate. In regard to the false prophet, and the nature of this alliance (see the comments on Revelation 16:13).

That wrought miracles before him. That is, the false prophet had been united with the beast in deceiving the nations of the earth (see the comments on Revelation 16:14).

With which he deceived them that had received the mark of the beast (see the comments on Revelation 13:16-18).

By these deceptions they had been deceived; that is, they had been led into the alliance and had been sustained in their opposition to the truth. The whole representation is that of an alliance to prevent the spread of the true religion, as if the Papacy and Islam were combined, and the one was sustained by the pretended miracles of the other.

There would be a practical opposition against the reign of the Son of God, as if these great powers should act in concert, and as if the peculiar claims which each set up in behalf of its own Divine origin became a claim which went to support the whole combined organization.

These both were cast alive into a lake of fire. The beast and the false prophet. That is, the overthrow will be as striking, and the destruction as complete, as if the leaders of the combined armies should be taken alive and thrown into a pit or lake that burns with an intense heat.

There is no necessity for supposing that this is to be literally inflicted, for the whole scene is symbolical. This means that the destruction of these powers would be as complete as if they were thrown into such a burning lake. (Compare to the comments on Revelation 14:10-11).

Burning with brimstone. Sulphur—the usual expression to denote intense heat, and especially as referring to the punishment of the wicked (see the comments on Revelation 14:10).