What does Isaiah 20:6 mean?
Isaiah has looked forward in time to when the Assyrians will fully defeat Egypt. The people will be stripped and marched away into captivity (Isaiah 20:4). The point of this powerful image is to convince God's people in Judah to not put their trust in Egypt (Isaiah 20:5). Only the Lord Himself is worthy of such confidence.The prophet turns to a response of the people who lived along the coastlands. These were the nations who were trusting in Egypt to provide them protection against the ravenous Assyrians. When they see the Egyptians stripped down and being marched away as prisoners of war, they will recognize that they have no other hope for escape. The ones they trusted are defeated. How can they hope to escape a similar fate?
The Lord does not want Judah to find themselves in the same position asking this same question. He wants them to know and believe that they can trust the Lord, and Him alone, to save them from their enemies. In the case of the Assyrians, the Lord did exactly that. When Jerusalem was besieged by Sennacherib and a massive army of Assyrians, the invading force was suddenly killed in the middle of the night by the angel of the Lord (Isaiah 37:33–38; 2 Kings 19:32–36).
Isaiah 20:1–6 describes a specific moment in history: 711 BC, when the Assyrian army crushed and took possession of the rebellious city of Ashdod. At the command of the Lord, Isaiah had been walking around without his outer garment or sandals to demonstrate how the Egyptians will look when they are also conquered by the Assyrians. Those counting on Egypt's protection will have nowhere to hide. Judah must trust the Lord to protect them and not any foreign nations.
The defeat of the Philistine city of Ashdod by the Assyrian king Sargon is the fulfillment of a strange sign. At the Lord's command, Isaiah spent three years regularly walking around barefoot and without his outer garment. This is to show what the Egyptian captives will look like once Assyria defeats them. Then all who boasted Egypt would protect them from Assyria will lose that confidence. The Lord wants Judah to trust Him to save them and not to look to other nations, or their gods.