Revelation 9:21

neither repented they of their murders nor of their sorceries nor of their fornication nor of their thefts.

The description of the great masses of horsemen enhances the general effect of the passage, to emphasize the terror and destruction of this great plague: And thus I saw the horses in the vision and those that sat upon them, having coats of mail, of fire and jacinth and brimstone; and the heads of the horses resembled heads of lions, and out of their mouth there went forth fire and smoke and sulfur. Here a host of attacking horsemen is described, with their armor gleaming red, dark-blue, and yellow. They were the instruments of divine wrath. No power on earth alone could stop the robbing and the murdering and the burning of these fiends. The heads of lions which the heads of their horses resembled showed the terrible power, the horrible anger which filled the hearts of the Mohammedan hordes, fire and smoke and sulfur issuing out of their mouths: By these three plagues were killed the third part of men, by the fire and the smoke and the sulfur which went forth out of their mouths. It was and is a murderous fanaticism with which the followers of Mohammed wage war, all the abominations of the abyss of hell being employed by them in their attempt to spread their false doctrine.

It is as St. John writes: For the power of the horses lies in their mouths and in their tails; for their tails resemble serpents, having heads, and with them they do injury. That is the secret of the power of this false prophet, the false, alluring doctrine which comes forth from his mouth. The tongues of his teachers are truly inflamed of hell with a disastrous fire, a veritable mystery of iniquity. The old serpent, Satan himself, is their inspiration, and wherever they lift their heads, injury and destruction follows.

And now John makes an almost incredible statement: And the rest of men, that were not killed in these plagues, yet repented not of the works of their hands, not to worship demons and idols of gold and of silver and of brass and of stone and of wood, which can neither see nor hear nor walk; and they repented not of their murders nor of their magic arts nor of their fornications nor of their thefts. Even as Pharaoh hardened his heart in spite of the many evidences of God's power performed in his sight, even as the children of Israel in the wilderness refused again and again to turn to the Lord in true repentance, in spite of the many miracles by which He sought to influence them, thus it has ever been in the history of the world. The Lord may send ever so many plagues, wars, pestilences, famines, and yet, as soon as He withdraws His chastening hand, men harden their hearts once more and refuse to repent of the works of their hands, of their idolatry, of their abuse of the name of God, of their murders and adulteries and robberies, hath great and small. Truly, this is a description of the abyss of human depravity, such a picture as we see but rarely in its entirety, although glimpses are seen often enough in these last days before the coming of the Lord in glory.

Summary

The prophet, in the description of the falling star and of the hordes of locusts swarming up from the pit of hell, draws a picture of some of the chief false teachers that have ever vexed Christianity; and, in a Similar manner, in the countless horsemen coming from the Euphrates, foretells the rise of Mohammedanism with its fake doctrines and all its attendant horrors.