Isa 8:5 The LORD spake also unto me again, saying,
Isa 8:6 Forasmuch as this people refuseth the waters of Shiloah that go softly, and rejoice in Rezin and Remaliah's son;
Isa 8:7 Now therefore, behold, the Lord bringeth up upon them the waters of the river, strong and many, even the king of Assyria, and all his glory: and he shall come up over all his channels, and go over all his banks:
Jerusalem was once named Shiloh, the stream of water that ran from Mount Zion was called Shiloah.
"The little stream of Shiloah sprung from Mount Zion on the southwesterly side of Jerusalem. It flowed as softly as oil without any murmur. Jerusalem's existence and continuation depended on it." (Bultema)
Judah had forsaken the God of Mount Zion and the living waters, for the gods of Assyria, where flowed the mighty Tigris and Euphrates rivers. The LORD uses a metaphor to contrast the gentle peace of God's spirit, flowing smoothly from Mount Zion to the hoards of Assyria, rushing over them like a river overflowing it's banks. Peace is found in the God of Israel, when they worship and obey Him.
Isa 8:8 And he shall pass through Judah; he shall overflow and go over, he shall reach even to the neck; and the stretching out of his wings shall fill the breadth of thy land, O Immanuel.
The armies of Assyria would pass over Judah and onto Syria, with destructive force. The ten Northern tribes of Israel would be conquered and no longer exist as a nation, but Judah would survive. King Hezekiah and Jerusalem survived because Hezekiah gave them the gold and silver from the temple. They had an arrangment.
2 Ki 18:13 Now in the fourteenth year of king Hezekiah did Sennacherib king of Assyria come up against all the fenced cities of Judah, and took them.
2 Ki 18:14 And Hezekiah king of Judah sent to the king of Assyria to Lachish, saying, I have offended; return from me: that which thou puttest on me will I bear. And the king of Assyria appointed unto Hezekiah king of Judah three hundred talents of silver and thirty talents of gold.
2 Ki 18:15 And Hezekiah gave him all the silver that was found in the house of the LORD, and in the treasures of the king's house.
2 Ki 18:16 At that time did Hezekiah cut off the gold from the doors of the temple of the LORD, and from the pillars which Hezekiah king of Judah had overlaid, and gave it to the king of Assyria.
...thy land, O Immanuel.
The prophesy gives the rightful owner of the land of Jerusalem as Immanuel; God owned the land. God would come again, Immanuel, King Jesus to inherit the land in the end times. The people of Judah were looking for this king to rule in the first coming, but first he must have gone to the cross, to cleanse us from our sins. O Immanuel, what a savior you are.
Isa 8:9 Associate yourselves, O ye people, and ye shall be broken in pieces; and give ear, all ye of far countries: gird yourselves, and ye shall be broken in pieces; gird yourselves, and ye shall be broken in pieces.
Resist the Assyrians and you will be broken to pieces, speaking to Syria, Israel and Judah. Why? Because God is using Assyria against you, to chastise you. You would not obey God, so he is sending an enemy nation, even if the nation does not believe in God, he can use them to punish those he chooses to correct. Are we listening to this?
Isa 8:10 Take counsel together, and it shall come to nought; speak the word, and it shall not stand: for God is with us.
As a messenger of God, Isaiah warns them not to counsel together, no cabinet meetings on how to defend themselves or defeat the enemy, because God has spoken. His word is with them and He is well aware of what is coming. It is the will of God.