stoma

This is the plain, physical meaning. The mouth is the part of the body food and drink go into and the part an animal can bite with. The New Testament uses it for an ordinary human mouth (the coin in the fish's mouth, vinegar lifted to Jesus' lips), for fierce animal mouths shut or escaped (the lions Daniel faced, the bit set in a horse's mouth), and for the terrifying mouths of the visionary creatures in Revelation, out of which pour fire, smoke, water, or foul spirits.

Because the mouth is an opening, the same word stretches naturally to the picture of the earth opening its "mouth" to swallow the flood the dragon spews. That is the one place the word names a gap in something other than a living body, and it works only because everyone can picture a mouth as a hole that takes things in.

Keep this sense distinct from the next one. Here the mouth is simply the organ, and what matters is that something physically goes into it or comes out of it, not that words are spoken.

This is the figure of speech that stands behind most New Testament uses. Naming the mouth is a vivid way of naming what a person says, the way English speaks of someone with a foul mouth or quotes a person from his own mouth. To open the mouth is to begin to speak or teach, and what comes out of the mouth, blessing or cursing, exposes the heart behind it.

A recurring biblical pattern uses the phrase through the mouth of someone to mean that God spoke His message by means of that person: the prophets, David, an apostle. The point is not the lips themselves but that a true word was delivered through a human voice. The same idea lets confession with the mouth stand for owning a belief out loud, and lets every mouth being stopped mean no one is left with anything to say in his own defense.

Revelation pushes the figure to its limit: the sharp sword coming out of the exalted Christ's mouth is His spoken word of judgment, and He destroys the lawless one with the breath of His mouth. The weapon is His speech, not a literal blade.

Greek, like Hebrew, can call the cutting edge of a sword its mouth, picturing the blade as something that devours those it strikes. When people fall by the mouth of the sword they are cut down in battle or slaughter.

This is a fixed idiom, not a fresh comparison, and the New Testament keeps it close to its Old Testament background. It names the instrument of violent death, with no thought of a literal mouth at all.