I will disguise myself - Ahab had probably heard of Ben-hadad's order to his captains 1 Kings 22:31.

I will disguise myself - Probably he had heard of the orders given by Ben-hadad to his thirty-two captains, to fight with the king of Israel only; that is, to make their most powerful attack where he commanded, in order to take him prisoner, that he might lead him captive whose captive he formerly was; and therefore he disguised himself that he might not be known.

But put thou on thy robes - What is meant by this? He could not mean, "Appear as the king of Judah, for they will not molest thee, as the matter of contention lies between them and me;" this is Jarchi's turn. For if Jehoshaphat aided Ahab, is it to be supposed that the Syrians would spare him in battle? A general in the civil wars of England, when he had brought his army in sight of their foes, thus addressed them: "Yonder are your enemies; if you do not kill them, they will kill you." So it might be said in the case of Jehoshaphat and the Syrians.

The Septuagint gives the clause a different and more intelligible turn: "I will cover (conceal) myself, and enter into the battle; και συ ενδυσαι τον ἱματισμον μου, but put thou on My robes." And does it not appear that he did put on Ahab's robes? And was it not this that caused the Syrians to mistake him for the king of Israel? 1 Kings 22:32.

And the king of Israel said unto Jehoshaphat, I will disguise myself, and enter into the battle,.... Change his clothes, his royal robes, and put on others, perhaps the habit of a common soldier; having, it may be, been informed by some deserters or spies, of the design of Benhadad against him. Abarbinel thinks the meaning is, that he would clothe himself with a coat of mail, and take to him the each of the instruments of war, and so go into the battle secure; this seems probable from 1 Kings 22:34 and this he might do to elude the prophecy of Micaiah:

but put thou on thy robes; his royal robes, or rather keep them on, that he might appear to be the chief commander of the army. There seems to be a good deal of insincerity and treachery in this conduct of Ahab's, whatever honour he might pretend to Jehoshaphat, or safety he might promise him in such a situation; his view seems to be to save himself at the hazard of the life of Jehoshaphat, especially if the Septuagint version could be established, "and put on my clothes"; which is natural enough, but would have been too barefaced:

and the king of Israel disguised himself, and went into the battle; as if he had been a common soldier.

And even Ahab could not throw off a certain fear of the fulfilment of Micah's prophecy. He therefore resolved to go to the battle in disguise, that he might not be recognised by the enemy. ובא התהפּשׂ ("disguise myself and go into the battle," i.e., I will go into the battle in disguise): an infin. absol., - a broken but strong form of expression, which is frequently used for the imperative, but very rarely for the first person of the voluntative (cf. Ewald, 328, c.), and which is probably employed here to express the anxiety that impelled Ahab to take so much trouble to ensure his own safety. (Luther has missed the meaning in his version; in the Chronicles, on the contrary, it is correctly given.) לבשׁ ואתּה, "but do thou put on thy clothes." These words are not to be taken as a command, but simply in this sense: "thou mayest (canst) put on thy (royal) dress, since there is no necessity for thee to take any such precautions as I have to take." There is no ground for detecting any cunning, vafrities, on the part of Ahab in these words, as some of the older commentators have done, as though he wished thereby to divert the predicted evil from himself to Jehoshaphat. but we may see very clearly that Ahab had good reason to be anxious about his life, from the command of the Syrian king to the captains of his war-chariots (1 Kings 22:31) to fight chiefly against the king of Israel. We cannot infer from this, however, that Ahab was aware of the command. The measure adopted by him may be sufficiently accounted for from his fear of the fulfilment of Micah's evil prophecy, to which there may possibly have been added some personal offence that had been given on his part to the Syrian king in connection with the negotiations concerning the surrender of Ramoth, which had no doubt preceded the war. The thirty-two commanders of the war-chariots and cavalry are, no doubt, the commanders who had taken the place of the thirty-two kings (1 Kings 21:24). "Fight not against small and great, but against the king of Israel only," i.e., endeavour above all others to fight against the king of Israel and to slay him.

And the king of Israel said unto Jehoshaphat, I will disguise myself, and enter into the battle; but put thou on thy robes. And the king of Israel disguised himself, and went into the battle.

I will...: or, when he was to disguise himself, and enter into the battle

22:29-40 Ahab basely intended to betray Johoshaphat to danger, that he might secure himself. See what they get that join with wicked men. How can it be expected that he should be true to his friend, who has been false to his God! He had said in compliment to Ahab, I am as thou art, and now he was indeed taken for him. Those that associate with evil-doers, are in danger of sharing in their plagues. By Jehoshaphat's deliverance, God let him know, that though he was displeased with him, yet he had not deserted him. God is a friend that will not fail us when other friends do. Let no man think to hide himself from God's judgment. God directed the arrow to hit Ahab; those cannot escape with life, whom God has doomed to death. Ahab lived long enough to see part of Micaiah's prophecy accomplished. He had time to feel himself die; with what horror must he have thought upon the wickedness he had committed!