What does Isaiah 8:8 mean?
The Lord has described coming events using the metaphor of rivers. The people of Judah did not trust the Lord, depicted as a gently flowing "river", to protect them from their enemies to the north (Isaiah 8:6). Instead, Ahaz and Judah put their hope in the powerful king of Assyria and his armies. Continuing the metaphor, the Assyrian army is referred to as the Euphrates River. Ahaz, the king of Judah, likely planned to ask Assyria for aid against Israel and Syria. He didn't want God's confirming miracle (Isaiah 7:10–13) because he'd already planned to take matters into his own hands.At first, this may have seemed like the right choice. Symbolized by the mighty Euphrates River—which flowed in their homeland—the Assyrians swept over Israel and Syria, completely wiping out the threat to Judah. The people rejoiced over the defeat of those kings who threatened them. Yet, just as one would expect of a flooding river, the destruction does not stop at a convenient place. The powerful Assyrians would not be contained. They will overflow into Judah (Isaiah 8:7). Picturing Judah as a person and Assyria as a flood, the Lords says they will almost, but not quite, wipe out them out. The waters will rise chin-deep, leaving the land decimated, but the victim alive.
Next, the Lord seems to change metaphors. Now, rather than a flood, Assyria will be like a bird of prey, stretching out its wings over the entire land. It will fail to carry off its food in the end. The prey will escape.
The Lord ends His revelation to Isaiah with the words, "O Immanuel." It's possible that Isaiah's son was called by the name Immanuel, along with his other name, in fulfillment of the prophecy of Isaiah 7:14. Some commentators suggest, that this is a reference to the promised Messiah, Immanuel, to whom the land of Judah belongs. Still others see in the name it's deeper meaning, "God with us." The Assyrians would fail to fully drown or carry off the people of Judah because God is with them.
It is unclear if Tiglath-pileser continued his campaign into Judah immediately following his destruction of Israel and Syria. Some scholars believe the Lord's prophecy in this passage to point forward to the later Assyrian kings, Sargon and Sennacherib. The kings who eventually decimated Judah but failed to take Jerusalem, culminating in 701 BC, as described in Isaiah 37.