Jamieson, Fausset and Brown on Isaiah 8:8

8. pass through--The flood shall not stop at Syria and Samaria, but shall penetrate into Judea.

the neck--When the waters reach to the neck, a man is near drowning; still the head is not said to be overflowed. Jerusalem, elevated on hills, is the head. The danger shall be so imminent as to reach near it at Sennacherib's invasion in Hezekiah's reign; but it shall be spared (Is 30:28).

wings--the extreme bands of the Assyrian armies, fulfilled (Is 36:1; 37:25).

thy land, O Immanuel--Though temporarily applied to Isaiah's son, in the full sense this is applicable only to Messiah, that Judea is His, was, and still is, a pledge that, however sorely overwhelmed, it shall be saved at last; the "head" is safe even now, waiting for the times of restoration (Ac 1:6); at the same time these words imply that, notwithstanding the temporary deliverance from Syria and Israel, implied in "Immanuel," the greatest calamities are to follow to Judah.