The Lord shall rise up as in mount Perazim... — The point of the reference to David’s victories at Baal Perazim (2 Samuel 5:20; 1 Chronicles 14:11), and at Gibeon (1 Chronicles 14:16) is that then Jehuah had interposed on behalf of His people against their enemies. The “new and strange” work — the very paradox of prophecy — was that He would now rise up to overthrow His own people.
Related Commentaries of Isaiah 28:21
Isaiah 28:21
21 For the LORD shall rise up as in mount Perazim, he shall be wroth as in the valley of Gibeon, that he may do his work, his strange work; and bring to pass his act, his strange act.