91 Then the fifth angel sounded: And I saw a star fallen from heaven to the earth. To him was given the key to the bottomless pit. 2 And he opened the bottomless pit, and smoke arose out of the pit like the smoke of a great furnace. So the sun and the air were darkened because of the smoke of the pit. 3 Then out of the smoke locusts came upon the earth. And to them was given power, as the scorpions of the earth have power. 4 They were commanded not to harm the grass of the earth, or any green thing, or any tree, but only those men who do not have the seal of God on their foreheads. 5 And they were not given authority to kill them, but to torment them for five months. Their torment was like the torment of a scorpion when it strikes a man. 6 In those days men will seek death and will not find it; they will desire to die, and death will flee from them.
Matthew Henry's Commentary on Revelation 9:1-6
Commentary on Revelation 9:1-12
(Read Revelation 9:1-12)
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, 1 Corinthians 11:19. And early writers plainly refer this to the first great host of corrupters who overspread the Christian church.