But if thou wilt go, do it, be strong for the battle
An ironical expression; if thou wilt not be advised, take them with thee, and try what thou canst do; exert all thy courage, and use thy military skill, and mark the issue:
God shall make thee fall before the enemy;
notwithstanding the number of thy troops, and those of thy auxiliaries; though some take them to be spoken seriously, and read the words, "but go thou"; that is, alone, without the hired troops, and fight boldly and courageously; or otherwise "God shall make thee fall"
for God hath power to help and to cast down;
to help with a few, and to cast down with many; to help without the hired Israelites, and to cast down with them.