Albert Barnes Commentary 2 Chronicles 14:8

"And Asa had an army that bare bucklers and spears, out of Judah three hundred thousand; and out of Benjamin, that bare shields and drew bows, two hundred and fourscore thousand: all these were mighty men of valor." — 2 Chronicles 14:8 (ASV)

The men of Judah served as heavy-armed troops, while the Benjamites were light-armed. Their numbers accord well with those in 2 Chronicles 13:3. As the boundaries of Judah had been enlarged (2 Chronicles 13:19), and as there had been no war for at least ten years (2 Chronicles 14:1), the effective military force had naturally increased. It was 400,000; it is now 580,000.