Charles Ellicott Commentary Revelation 9:18

"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." — Revelation 9:18 (ASV)

By these three... It is better to read, From these three plagues were the third part of mankind slain, by the fire and the smoke and the brimstone which goes forth out of their mouths. For the power of the horse is in their mouth, and in their tails, for their tails were like serpents, having heads, and with them they hurt (or, injure).

The destructive power in this vision is in the mouth and tail; in the last trumpet-vision, it was in the tail only (Revelation 9:10). The devastating power is increased: the foes come swift as horsemen, strong as lions, venomous as serpents, breathing forth elements that blind and burn with deadly power. We have, then, forces that are mighty, malicious, and relentless, and that are called forth against mankind for their sins of worldliness .

Not only once in the history of the world have such powers been let loose. The desolations wrought by invading hordes—the force and ferocity of Turkish power establishing itself in Europe and threatening the power of Christendom—the widespread terror and slaughter promoted by the outbreak of the spirit of unrestrained violence in France, followed by reckless war, may illustrate such a vision as the present one.

But the main teaching of it is the never-failing truth that the spirit of worldliness provokes its own punishment, wherever it may exist. Its retribution is in a form that serves to reveal what latent power of destruction lurks behind every sin, and what hidden spiritual foes there are to intensify human passions and to increase human misery.