Albert Barnes Commentary 1 Samuel 15:33

"And Samuel said, As thy sword hath made women childless, so shall thy mother be childless among women. And Samuel hewed Agag in pieces before Jehovah in Gilgal." — 1 Samuel 15:33 (ASV)

Hewed in pieces - This term is found only in this passage. Samuel thus executed the חרם chērem (1 Samuel 15:3), which Saul had violated. In doing so, he both saved the nation from the guilt of a broken oath and gave a final example to Saul—though apparently in vain—of uncompromising obedience to the commandments of God.

There is something awe-inspiring in the majesty of the prophet rising above and eclipsing that of the king (Compare 1 Kings 21:20, Jeremiah 38:14 and following, Daniel 2:46, and Daniel 4:27).