John the Apostle
Revelation 9:19ESV·traditional attribution

For the power of the horses is in their mouths and in their tails, for their tails are like serpents with heads, and by means of them they wound.

Matthew Henry Presbyterian @wholebiblehenry

Here let us consider the preface to this vision, and then the vision itself. I. The preface to this vision: A voice was heard from the horns of the golden altar, Rev 9:13, Rev 9:14. Here observe, 1. The power of the church's enemies is restrained till God gives the word to have them turned loose. 2.

Commenting on Revelation 9:13-21

John Gill Reformed Baptist @doctorgill

For their power is in their mouth,.... In what proceeded out of their mouth, or seethed to do so; in their guns, and what came out of them: and in their tails; which may design their foot soldiers, which were as the tail to their horse, and who sometimes did great service; or their way of fighting when they fled, by casting up arrows into...

Albert Barnes Presbyterian @notesbybarnes

Verse 19. For their power is in their mouth. That is, as described, in the fire, smoke, and brimstone that proceeded out of their mouths. What struck the seer as remarkable on looking on the symbol was, that this immense destruction seemed to proceed out of their mouths.