Charles Ellicott Commentary 1 Kings 20:42

"And he said unto him, Thus saith Jehovah, Because thou hast let go out of thy hand the man whom I had devoted to destruction, therefore thy life shall go for his life, and thy people for his people." — 1 Kings 20:42 (ASV)

A man whom I appointed—properly, a man under my curse. The rash action of Ahab, like the deliberate disobedience of Saul (1 Samuel 15:0), may have been due partly to compassion, partly to weakness. In either case it had no right to stand unauthorized between God’s judgment and him on whom it was pronounced; for even soft-heartedness, as in the case of Eli, may be treason to the cause of righteousness. The prophet (like Elisha, in 2 Kings 13:19) speaks partly as a patriot, jealous—and, as the event proved, with a sagacious jealousy—of the leniency which left the deadly enemy of Israel unsubdued; but he speaks also as the representative of God’s stern and righteous judgment, which Ahab, after signal deliverance, had treated as of no account. (For the fulfillment of his words, see 1 Kings 22:34–36.)