John Calvin Commentary Zechariah 14:15

"And so shall be the plague of the horse, of the mule, of the camel, and of the ass, and of all the beasts that shall be in those camps, as that plague." — Zechariah 14:15 (ASV)

Zechariah in this verse raises up the minds of the godly, so that they might know that their own efforts would accomplish nothing, but that after trying everything, they would be put to flight by the power of God. And thus it becomes more evident what has been twice repeated—that the Prophet does not simply announce calamities to terrify the Jews, but to encourage them to steadfastness, so that they might boldly rejoice, even when nearly overwhelmed by a vast heap of evils.

The meaning, then, is—that after Satan had tried everything to bring about the ruin of the Church, and the ungodly had left nothing undone, there would still be a successful outcome for the faithful. For God would execute his vengeance not only on humans, but also on horses, camels, and on all cattle. And since God’s wrath would burn against all animals, which are innocent in themselves, it can be concluded with certainty that those enemies who had provoked him by their cruelty could not escape his judgment and the punishment described here by the Prophet. He then adds—