What does Revelation 9:18 mean?
Prior verses depicted an army numbering two hundred million, unleashed along with four specially-prepared angels (Revelation 9:13–17). Some see John's description, including references to fire and sulfur coming from their "mouths" as an attempt to describe modern warfare coming from a man who'd never seen anything more advanced than catapults and giant crossbows. Others prefer to interpret this as a more supernatural or literally demonic force. John reports in this verse that the fire, smoke, and sulfur from the horses' mouths kills one third of mankind. Combined with the earlier death of one fourth of humanity (Revelation 6:7–8), the tribulation has so far halved earth's population.The idea that literal smoke and fire could be used as weapons by an army is not farfetched. Smoke inhalation and fire can kill, and so can the fumes of burning sulfur. This result is reminiscent of the destruction of Sodom and Gomorrah. The Lord rained on them sulfur and fire (Genesis 19:24). All the residents of those cities were destroyed except Lot, his wife, and their two daughters (Genesis 19:25; 2 Peter 2:7). Second Peter 2:6 reports that "by turning the cities of Sodom and Gomorrah to ashes he condemned them to extinction, making them an example of what is going to happen to the ungodly." A similar fate awaits unbelievers in the tribulation, when fire, smoke, and sulfur issues forth from the invading army's horses' mouths.
Some interpreters suggest that the fifth and sixth trumpet judgments will have no impact on those who come to faith in Christ after the rapture. The locust-like army from earlier in this chapter was explicitly told to target only unbelievers. However, there is no specific mention that the four angels (Revelation 9:14) or the massive army (Revelation 9:15–16) are given any such restriction. Those who think God will spare believer from these events point to the protection of God's people in the land of Goshen when God unleashed the plagues on Egypt (Exodus 9:22–26; 11:4–7).