John Calvin Commentary Isaiah 21:15

"For they fled away from the swords, from the drawn sword, and from the bent bow, and from the grievousness of war." — Isaiah 21:15 (ASV)

For they flee from the face of the swords. He means that the calamity will be dreadful, and that the Arabians will have good reason for fleeing, because the enemies will pursue them with arms and with swords, so that they will have no other way of ensuring their safety than by fleeing.

The reason why he foretells this defeat is plain enough; for it was necessary that the Jews should obtain early information about what would happen long after, so that they might learn that the world is governed by the providence of God and not by chance, and also that they should be taught by the example of others to behold God as the judge of all nations, wherever they looked.

We do not know, and history does not inform us, whether or not the Arabians were enemies of the Jews. However that may be, it is certain that these things are spoken for the consolation of the godly, that they may behold the justice of God towards all nations, and may acknowledge that his judgment-seat is at Jerusalem, from which he will pronounce judgment on the whole world.