The land of Judah shall be a terror unto Egypt. In Manasseh's reign Judaea became subject to Assyria, and had to take part in the hostile expeditions, which both Esarhaddon and his son, Asshurbanipal, conducted against Egypt.
Egypt had to keep her eye on Judaea continually, to see when danger was approaching her. If is not likely that Isaiah's prophecies caused the "terror" here spoken of. Every one that maketh mention thereof shall be afraid; rather, when any one maketh mention thereof, they shall turn to him in fear.
The very mention of Judaea by any one shall cause fear, because they will expect to hear that an expedition has started, or is about to start, from that country. Because of the counsel of the Lord of hosts.
This is how Isaiah views the Assyrian attacks on Egypt, not how the Egyptians viewed them. The fear felt by the Egyptians was not a religious fear. They simply dreaded the Assyrian armies, and Judaea as the country from which the expeditions seemed to issue.