He said — He joins with him in this war; because the war was just in itself, and convenient for Jehoshaphat, both in the general, that revolters should be chastised: lest the examples should pass into his dominions, and the Edomites be encouraged to revolt from him, as they did from his son; and in particular, that the Moabites should be humbled, who had invaded his land before this time, 2 Chronicles 20:1, and might do so again if they were not brought low; for which a fair opportunity now offered.
Related Commentaries of 2 Kings 3:7
2 Kings 3:7
7 And he went and sent to Jehoshaphat the king of Judah, saying, The king of Moab hath rebelled against me: wilt thou go with me against Moab to battle? And he said, I will go up: I am as thou art, my people as thy people, and my horses as thy horses.