If the present text is regarded as sound, this passage must be taken ironically. But most recent commentators supply a second negative, and render it: “But go thou alone, act, be strong for the battle - God shall then not make thee to fall.”
Related Commentaries of 2 Chronicles 25:8
2 Chronicles 25:8
8 But if thou wilt go, do it, be strong for the battle: God shall make thee fall before the enemy: for God hath power to help, and to cast down.