In verse 6, the Lord had been referred to as the “waters of Shiloah.” Isaiah continues the water theme by likening the king of Assyria to a great river. The Assyrians were on the other side of the Euphrates River, and this is probably the river to which Isaiah is referring. At any rate, the armies of the Assyrians overcome the kingdom of Israel like the flood of an overflowing river. The destruction would completely overcome them. The kingdom of Judah would also be attacked but would survive the flood of Assyrians. The imagery is that the floodwaters ‘shall reach even to the neck’ (v. 9)—almost drowning Judah. The fact that the head remained above water means that the head of Judah, Jerusalem, would be spared. (See Commentary for 2 Ne. 17:17).
“Isaiah describes and then contrasts two forms of waters—the soft, rolling waters of Shiloah, located near the temple mount of Jerusalem, and the waters of the Euphrates, a great river that often floods out of control. The waters of Shiloah are controlled and inviting, whereas the Euphrates is dangerous and destructive. The waters of Shiloah bring life to those who drink them; the Euphrates brings death to those who are swept up in its flood. Isaiah’s images of the two waters are symbolic: the former represents Jesus, the King of Heaven, who is likened to the waters of life; the latter is the king of Assyria, who leads his great, destructive armies and ’cover the earth [like a flood … and] destroy the inhabitants thereof’ (Jer. 46:8Jer. 46:8). Inasmuch as the inhabitants of Judah had rejected Jesus, or the waters of Shiloah, the Lord set upon them the king of Assyria, or the strong and mighty waters of the river that would overflow their banks and cover the entire land with its destruction.” (Donald W. Parry, Jay A. Parry, and Tina M. Peterson, Understanding Isaiah [Salt Lake City: Deseret Book Co., 1998], 83 as taken from Commentaries on Isaiah in the Book of Mormon, ed. by K. Douglas Bassett, [American Fork, UT: Covenant Publishing Co., 2003], 137)