What does Isaiah 20:3 mean?
The sequence of events in Isaiah 20 seems to be as follows: The Lord tells Isaiah to walk around stripped of his shoes and outer garments (Isaiah 20:2). Three years later, the Assyrians defeated the Philistine city of Ashdod. Ashdod had made an alliance with Egypt against the Assyrians. But when that attack came from Assyria, Egypt did not help (Isaiah 20:4–5).Now the Lord reveals the point of Isaiah's humiliating exposure. His physical appearance was a symbol against Egypt and Cush. A "sign and portent" is a prophecy about something big that is going to happen, usually something momentous and tremendously negative. In this case, the fulfillment of that sign would show that God was right. And a further sign that Judah should not rely on Egypt to save them from the Assyrians.
Cush, sometimes called Nubia, was south of Egypt. It was also known as Ethiopia, though this is not the same nation as modern-day Ethiopia. An Ethiopian dynasty ruled Egypt at this time. Cush and Egypt would suffer the same fate together at the hands of the Assyrians.