John Gill Commentary 2 Chronicles 28:6

"For Pekah the son of Remaliah slew in Judah a hundred and twenty thousand in one day, all of them valiant men; because they had forsaken Jehovah, the God of their fathers." — 2 Chronicles 28:6 (ASV)

For Pekah son of Remaliah Who was at this time king of Israel:

slew in Judah an hundred and twenty thousand in one day , which were all

valiant men ; a great slaughter to be made at one time, and of valiant men, but not so great as that in (2 Chronicles 13:17) ,

because they had forsaken the Lord God of their fathers ; this was not a reason with Pekah for slaying them, he himself being an idolater, but why the Lord suffered them to be slain by him.