Charles Ellicott Commentary 2 Kings 19:32-34

"Therefore thus saith Jehovah concerning the king of Assyria, He shall not come unto this city, nor shoot an arrow there, neither shall he come before it with shield, nor cast up a mound against it. By the way that he came, by the same shall he return, and he shall not come unto this city, saith Jehovah. For I will defend this city to save it, for mine own sake, and for my servant David`s sake." — 2 Kings 19:32-34 (ASV)

This may be, as Mr. Cheyne supposes, an after addition to the original prophecy. Isaiah may have spoken it a little later, in which case it was quite natural for an editor to append it here, as belonging to the same crisis. But it seems better to see here a return to the subject of the king of Assyria, after the parenthetic address to Hezekiah. The repetition of 2 Kings 19:28 in 2 Kings 19:33 favours this view.