rod ... broken - The yoke imposed by Uzziah (2Ch 26:6) was thrown off under Ahaz (2Ch 28:18).
serpent’s root - the stock of Jesse (Isa 11:1). Uzziah was doubtless regarded by the Philistines as a biting “serpent.” But though the effects of his bite have been got rid of, a more deadly viper, or “cockatrice” (literally, “viper’s offspring,” as Philistia would regard him), namely, Hezekiah awaits you (2Ki 18:8).