The men of Israel fled before Judah, and God gave them into their hand.
We do not find that Jeroboam offered to make any answer at all to Abijah's speech. Though it was much to the purpose, he resolved not to heed it, and therefore he heard it as though he heard it not. He came to fight, not to dispute. The longest sword, he thought, would determine the matter, not the better cause.
Commenting on 2 Chronicles 13:13-22
And Abijah and his people slew them with a great slaughter,.... As they fled, pursuing them: so there fell down slain of Israel five hundred thousand chosen men; such a slaughter as is not to be met with in any history, as Josephus (s) observes; though Abarbinel wonders he should say so, and affirms that he had read of larger numbers slain at once; but...
2Ch 13:16-17 So Abijah and his people inflicted a great blow (defeat) on the Israelites, so that 500,000 of them, i.e., more than the half of Jeroboam’s whole army, fell.
Commenting on 2 Chronicles 13:16-17