Matthew Henry Commentary Revelation 9:13-21

"And the sixth angel sounded, and I heard a voice from the horns of the golden altar which is before God, one saying to the sixth angel that had one trumpet, Loose the four angels that are bound at the great river Euphrates. And the four angels were loosed, that had been prepared for the hour and day and month and year, that they should kill the third part of men. And the number of the armies of the horsemen was twice ten thousand times ten thousand: I heard the number of them. And thus I saw the horses in the vision, and them that sat on them, having breastplates [as] of fire and of hyacinth and of brimstone: and the heads of lions; and out of their mouths proceedeth fire and smoke and brimstone. By these three plagues was the third part of men killed, by the fire and the smoke and the brimstone, which proceeded out of their mouths. For the power of the horses is in their mouth, and in their tails: for their tails are like unto serpents, and have heads; and with them they hurt. And the rest of mankind, who were not killed with these plagues, repented not of the works of their hands, that they should not worship demons, and the 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 sorceries, nor of their fornication, nor of their thefts." — Revelation 9:13-21 (ASV)

The sixth angel sounded, and here the power of the Turks seems to be the subject. Their time is limited. They not only killed in war but also brought a poisonous and ruinous religion.

The antichristian generation did not repent under these dreadful judgments. From this sixth trumpet, learn that God can make one enemy of the church a scourge and a plague to another.

The idolatry in the remains of the eastern church and elsewhere, and the sins of professed Christians, make this prophecy and its fulfillment more remarkable.

And the attentive reader of Scripture and history, may find his faith and hope strengthened by events which, in other respects, fill his heart with anguish and his eyes with tears.

This occurs while he sees that those who escape these plagues do not repent of their evil works but continue with idolatries, wickedness, and cruelty, until wrath comes upon them to the utmost.