Charles Ellicott Commentary 2 Kings 3:7

"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, my horses as thy horses." — 2 Kings 3:7 (ASV)

Will you go. —So Ahab asks Jehoshaphat in 1 Kings 22:4, and he replies as here, I am as you are, etc. This indicates that the present section was originally composed by the same hand as 1 Kings 20:1–34; 1 Kings 22:1–37 (Thenius). Jehoshaphat assented, in spite of the prophetic censures of his alliance with Ahab and Ahaziah (2 Chronicles 19:2; 2 Chronicles 20:37); perhaps because he was anxious to inflict further punishment on the Moabites for their inroad into Judah (2 Chronicles 20:0), and to prevent any recurrence of the same (Keil).

Against Moab to battle? —Or, into Moab to the war?