A prophet's strange and physical actions often serve as a living, tangible prophecy, painting a clear picture of the fate awaiting great empires. When God commands a prophet to perform a physical symbolic action, the decree becomes absolute and irreversible. This stands in sharp contrast to regular prophecies of doom, which can often be canceled if people repent [מלבי״ם].
There are different views regarding when God actually explained the meaning of this unusual behavior. Some suggest that the divine explanation was given to the prophet only after he had already walked naked and barefoot [רד״ק]. Others argue that the message was clear from the very beginning. God knew in advance that the siege of Ashdod would last for three years, and Isaiah informed the people of Judah that his behavior throughout this entire period was a live demonstration of the future fate of the captives [שד״ל].
The primary approach among commentators is that the timeframe of three years indicates that at the end of this period, the king of Assyria would lead the captives of Egypt and Cush away naked and barefoot. Historically, the conquest of Ashdod occurred three years before the downfall of Sennacherib. This downfall happened exactly as he was besieging Jerusalem, having brought the captives of Egypt and the king of Cush in collars [רש״י]. Another perspective suggests that Egypt would endure continuous suffering for three full years, or that the events would unfold exactly three years from that day [אבן עזרא].
The terms used to describe the prophet's actions—a sign and a wonder—are seen by some simply as synonyms meaning a symbol [מצודת ציון]. However, others draw a clear distinction between the two. A sign is a symbol pointing to a future reality, showing that the Egyptians would eventually walk naked just as the prophet did. A wonder, on the other hand, refers to the sheer shock and amazement that gripped anyone who witnessed the prophet's bizarre and highly unusual behavior [מלבי״ם].
An additional layer of meaning suggests that this shocking display was originally directed at the people of Israel. It was meant as a hint that they would face exile as a consequence of placing their trust in Egypt. Yet, because of Isaiah's deep sorrow and his prayers, the decree against Israel was canceled for the time being, and the harsh fate was redirected toward Egypt and Cush. Even so, it remained clear that if Israel would return to God with complete repentance, the underlying decree could be entirely abolished [חומת אנך].