Jamieson, Fausset and Brown on 2 Chronicles 25:7-8

7-8. there came a man of God--sent to dissuade Amaziah from the course he was following, on the ground that "the Lord is not with Israel." This statement was perfectly intelligible to the king. But the historian, writing long after, thought it might require explanation, and therefore added the comment, "with all the children of Ephraim." Idolatry had long been the prevailing religion in that kingdom, and Ephraim its headquarters. As to the other part of the prophet's advice (2Ch 25:8), considerable obscurity hangs over it, as the text stands; and hence some able critics have suggested the insertion of "not" in the middle clause, so that the verse will be thus: "But if thou wilt go [alone], do, be strong for the battle; God shall not make thee fall before the enemy."