John Calvin Commentary Isaiah 7:18

"And it shall come to pass in that day, that Jehovah will hiss for the fly that is in the uttermost part of the rivers of Egypt, and for the bee that is in the land of Assyria." — Isaiah 7:18 (ASV)

And it shall be in that day. The Jews thought that the Assyrians were bound by their league with them; but the Prophet ridicules this folly, and declares that they will be ready at God’s command to drive them in any direction that he thinks fit. Yet instead of command, he uses the metaphor hiss, alluding to the climate of those kingdoms about which he speaks; for Egypt abounds in flies, because the country is hot and marshy; and when the air is both hot and moist, a great abundance of flies is produced.

Assyria, on the other hand, abounded in bees; and when he says that he will bring them by a hiss, he alludes to the natural habits of bees and flies, but he means that he will find no difficulty in sending them. As if he had said, “There will be no need of great exertion; for as soon as I give the sign, they will instantly run.” In this way, he shows what efficacy belongs to his secret operation or design, that by a hiss he compels the most powerful nations to obey.