Complete Commentary on the Whole Bible, by Matthew Henry, at sacred-texts.com
(Rev 9:1-12) The fifth trumpet is followed by a representation of another star as falling from heaven and opening the bottomless pit, out of which come swarms of locusts.
(Rev 9:13-21) The sixth trumpet is followed by the loosing of four angels bound in the great river Euphrates.
Upon sounding the fifth trumpet, a star fell from heaven to the earth. Having ceased to be a minister of Christ, he who is represented by this star becomes the minister of the devil; and lets loose the powers of hell against the churches of Christ. On the opening of the bottomless pit, there arose a great smoke. The devil carries on his designs by blinding the eyes of men, by putting out light and knowledge, and promoting ignorance and error. Out of this smoke there came a swarm of locusts, emblems of the devil's agents, who promote superstition, idolatry, error, and cruelty. The trees and the grass, the true believers, whether young or more advanced, should be untouched. But a secret poison and infection in the soul, should rob many others of purity, and afterwards of peace. The locusts had no power to hurt those who had the seal of God. God's all-powerful, distinguishing grace will keep his people from total and final apostacy. The power is limited to a short season; but it would be very sharp. In such events the faithful share the common calamity, but from the pestilence of error they might and would be safe. We collect from Scripture, that such errors were to try and prove the Christians, Co1 11:19. And early writers plainly refer this to the first great host of corrupters who overspread the Christian church.
The sixth angel sounded, and here the power of the Turks seems the subject. Their time is limited. They not only slew in war, but brought a poisonous and ruinous religion. The antichristian generation repented not 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, render this prophecy and its fulfilment more wonderful. 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, while he sees that men who escape these plagues, repent not of their evil works, but go on with idolatries, wickedness, and cruelty, till wrath comes upon them to the utmost.