C. F. Keil and Franz Delitzsch on 1 Samuel 15:33

1Sa 15:33

But Samuel pronounced the sentence of death upon him: “As thy sword hath made women childless, so be thy mother childless before women!” מנּשׁים is to be understood as a comparative: more childless than (other) women, i.e., the most childless of women, namely, because her son was the king. From these words of Samuel, it is very evident that Agag had carried on his wars with great cruelty, and had therefore forfeited his life according to the lex talionis. Samuel then hewed him in pieces “before the Lord at Gilgal,” i.e., before the altar of Jehovah there; for the slaying of Agag being the execution of the ban, was an act performed for the glory of God.