Israel had revolted against the Lord, but when they would return, He would defend them and fight for them, so that He could say of their enemy Assyria,
“‘Then Assyria shall fall by a sword not of man, and a sword not of mankind shall devour him. But he shall flee from the sword, and his young men shall become forced labor. He shall cross over to his stronghold for fear, and his princes shall be afraid of the banner,’ says the LORD, whose fire is in Zion and whose furnace is in Jerusalem” (Isaiah 31:8-9).
Clearly it would be the Lord doing these things, because He stood for Jerusalem, the capital of His people Israel, and He was a fire for them during the days of the Assyrian invasion, even as He was during the days when Egypt pursued Israel at the Red Sea.
Be faithful to the Lord, and watch what He does for you.