Albert Barnes Commentary Isaiah 19:17

"And the land of Judah shall become a terror unto Egypt; every one to whom mention is made thereof shall be afraid, because of the purpose of Jehovah of hosts, which he purposeth against it." — Isaiah 19:17 (ASV)

And the land of Judah - The fear and consternation of Egypt will be increased when they learn what events are occurring there, and what Yahweh has purposed in regard to it.

Will be a terror - This cannot be understood to mean that they were in danger from an invasion by the Jews, for at that time they were not at war, and Judah had no power to overrun Egypt. Jarchi and Kimchi suppose that the passage means that the Egyptians would hear what had occurred to the army of Sennacherib in its overthrow, and that they would be alarmed as if a similar fate was about to come upon them.

But the more probable interpretation is that which refers it to the invasion of Judah by Sennacherib. The Egyptians would know of that. Indeed, Sennacherib's leading design was to invade Egypt, and Judah and Jerusalem were to be destroyed only on the way to Egypt. When the Egyptians heard of Sennacherib's great preparations and his advance upon Judah , and knew that his design was to invade them, the land of Judah would be a terror, because they feared he would make a rapid descent upon them.

Vitringa, however, supposes that the sense is that the Egyptians, in their calamities, would remember the prophecies of Jeremiah and others regarding their punishment, which they had heard. He suggests they would remember that the prophecies concerning Judah had been fulfilled, and that Judah would thus be a terror to them because those predictions had come from Judah. This is plausible, and it may be the correct explanation.

Which he has determined against it - This refers either to Judah or Egypt, as the Hebrew allows for either interpretation. It may mean that they were alarmed at the counsel Yahweh had formed against Judah—a counsel apparently about to be executed by Sennacherib's invasion—and consequently feared an invasion themselves. Alternatively, it may mean they learned that Yahweh had formed a purpose of destruction against them, and Judah thus became an object of terror because the prophecies spoken there were certain to be fulfilled. The latter is the interpretation given by Vitringa, and perhaps is the most probable.