Commentary on the Bible, by Adam Clarke, [1831], at sacred-texts.com
Jehoshaphat joins affinity with Ahab, king of Israel, Ch2 18:1, Ch2 18:2; who invites him to assist him in the war against the Syrians, to which Jehoshaphat agrees, Ch2 18:3. They consult the prophets concerning the success of the war; and all, except Micaiah, promise Ahab victory, Ch2 18:4-17. Micaiah relates his vision concerning the lying spirit in the mouth of Ahab's prophets, Ch2 18:18-22. Zedekiah, a false prophet, opposes Micaiah; and Micaiah is put in prison, Ch2 18:23-27. Both the kings go against the Syrians; the confederate armies are defeated, and the king of Israel slain, Ch2 18:28-31.
Jehoshaphat had riches and honor - The preceding chapter gives ample proof of this.
Joined affinity with Ahab - Took his daughter Athalia to be wife to his son Joram.
To Ramoth-gilead - This place belonged to the Israelites, and was now held by the king of Syria.
The whole of this chapter is circumstantially explained in the notes on 1 Kings 22:1-53.
The king of Israel and Jehoshaphat - "Ahab consulted false prophets; but Jehoshaphat sought instruction from the presence of the Lord, and prayed at the entering in of Samaria; and before these all the false prophets prophesied lies." - Targum.
Then there came out a spirit - The Targum gives a strange gloss here: "Then the spirit of Naboth of Jezreel came out from the abode of the righteous, and stood before the Lord, and said, I will deceive him. And the Lord said, By what means? To which he answered, I will be a spirit of false prophecy in the mouth of his prophets. And the Lord said, Thou mayest then. But although the power of deceiving them is given unto thee, nevertheless it will not be lawful for thee to sit among the righteous; for whosoever shall speak falsely cannot have a mansion among the righteous. Therefore go forth from me, and do as thou hast said." - Targum.
I will disguise myself - See the note on Kg1 22:30.
But Jehoshaphat cried out - "Jehoshaphat cried, and the Word of the Lord brought him assistance." - Targum.
A certain man drew a bow - The Targum tells us who it was. "Now, Naaman, the captain of the host of the great king of Syria, drew a bow against him, (that the prophecy of Elijah the Tishbite, and of Micaiah the son of Imla, might be fulfilled), and smote the king of Israel between the heart and the caul of the liver, through the place where the coat of mail is joined." See the note on Kg2 5:1 for this tradition.
Stayed himself up - against the Syrians - There was a great deal of true personal courage and patriotism in this last act of the king of Israel: he well knew that if his troops found that he was mortally wounded, they would immediately give way, and the battle would not only be lost, but the slaughter would be great in the pursuit; therefore he stayed himself up till the evening, when the termination of the day must necessarily bring the battle to a close: and when this was done, the Israelites found that their king was slain, and so they left the field of battle to their foes. Thus Israel had a great loss, and the Syrians had got a great deliverance. Had it not been for this accident, the Syrians had probably been defeated. See on Kg1 22:36 (note).
In the notes referred to above, the quibbling predictions of false prophets and lying oracles are mentioned, and several instances given; and the whole account of the lying spirit going forth from the Lord to deceive Ahab, particularly considered. See especially the notes as above on Ch2 18:19 (note), Ch2 18:23-24 (note).
The reader should never forget a truth so very frequently occurring in the Bible, that God is repeatedly represented as doing what, in the course of his providence, he only permits to be done.