Assyria’s destruction of the northern kingdom of Israel will also bring waste and desolation to Judah. Gileadi’s translation of this passage reads: “The Lord will bring upon you and your people and your father’s house a day unlike any since Ephraim broke away from Judah—the day of the king of Assyria.”
The italicized “the day” is, Gileadi argues, implied as a parallel to the day “unlike any”—a day of political catastrophe. Given Isaiah’s penchant for poetic parallels, Gileadi’s reading continues his literary techniques better than a simple announcement that the Assyrian king would come.
Isaiah warns Ahaz that the Assyrian alliance will bring a few years of peace (the child eats butter and honey, v. 15) but it will eventually prove to be a curse on Judah unparalleled by any since the split of the kingdom among Solomon’s successors.