we will be with thee. Jehoshaphat was deceived by its seeming to be. "good work". But "good" works are only "prepared" works (Ephesians 2:10). It could not be "good" if done "with thee" (Compare 2 Chronicles 19:2). "Better is he that ruleth his spirit than he that taketh. city" (Proverbs 16:32). But Jehoshaphat did not "take it".
Related Commentaries of 2 Chronicles 18:3
2 Chronicles 18:3
3 And Ahab king of Israel said unto Jehoshaphat king of Judah, Wilt thou go with me to Ramothgilead? And he answered him, I am as thou art, and my people as thy people; and we will be with thee in the war.