Translate - "Go, say unto him, Thou shalt certainly live: howbeit the Lord hath showed me that he shall certainly die." i. e.," Say to him, what thou hast already determined to say, what a courtier is sure to say (compare 1-Kings 22:15), but know that the fact will be otherwise."

Thou mayest certainly recover: howbeit the Lord hath showed me that he shall surely die - That is, God has not determined thy death, nor will it be a necessary consequence of the disease by which thou art now afflicted; but this wicked man will abuse the power and trust thou hast reposed in him, and take away thy life. Even when God has not designed nor appointed the death of a person, he may nevertheless die, though not without the permission of God. This is a farther proof of the doctrine of contingent events: he might live for all his sickness, but thou wilt put an end to his life.

And Elisha said unto him, Go, say unto him, Thou mayest certainly (f) recover: howbeit the LORD hath shewed me that he shall surely die.
(f) Meaning that he would recover of this disease: but he knew that this messenger Hazael would slay him to obtain the kingdom.

And Elisha said unto him, go, say unto him, thou mayest certainly recover,.... That is, of the disease; and there was not only a probability that he might recover of it, it not being a mortal one, but a certainty that he should not die of it, as he did not, but die a violent death, which the prophet predicts in the next clause; though some take these words not as a command, what he should say, but as a prediction of what he would say; that he would go and tell him he should certainly recover, because he would not discourage him, though the prophet assures him in the next clause that he should die: there is a various reading of these words; we follow the marginal reading, but the textual reading is, "say, thou shall not certainly recover", or "in living live"; which agrees with what follows:
howbeit or "for"
the Lord hath showed me, that he shall surely die; though not of that sickness, nor a natural death, but a violent one, and that by the hand of this his servant, though he does not express it.

Go, say . . . Thou mayest certainly recover--There was no contradiction in this message. This part was properly the answer to Ben-hadad's inquiry [2-Kings 8:9]. The second part was intended for Hazael, who, like an artful and ambitious courtier, reported only as much of the prophet's statement as suited his own views (compare 2-Kings 8:14).

According to the Chethb חיה לא, Elisha's answer was, "Thou wilt not live, and (for) Jehovah has shown me that he will die;" according to the Keri חיה לו, "tell him: Thou wilt live, but Jehovah," etc. Most of the commentators follow the ancient versions, and the Masoretes, who reckon our לא among the fifteen passages of the O.T. in which it stands for the pronoun לו (vid., Hilleri Arcan. Keri, p. 62f.), and some of the codices, and decide in favour of the Keri. (1) because the conjecture that לו was altered into לא in order that Elisha might not be made to utter an untruth, is a very natural one; and (2) on account of the extreme rarity with which a negative stands before the inf. abs. with the finite verb following. But there is not much force in either argument. The rarity of the position of לא before the inf. abs. followed by a finite verb, in connection with the omission of the pronoun לו after אמר, might be the very reason why לא was taken as a pronoun; and the confirmation of this opinion might be found in the fact that Hazael brought back this answer to the king: "Thou wilt live" (2-Kings 8:14). The reading in the text לא (non) is favoured by the circumstance that it is the more difficult of the two, partly because of the unusual position of the negative, and partly because of the contradiction to 2-Kings 8:14. But the לא is found in the same position in other passages (Genesis 3:4; Psalm 49:8, and Amos 9:8), where the emphasis lies upon the negation; and the contradiction to 2-Kings 8:14 may be explained very simply, from the fact that Hazael did not tell his king the truth, because he wanted to put him to death and usurp the throne. We therefore prefer the reading in the text, since it is not in harmony with the character of the prophets to utter an untruth; and the explanation, "thou wilt not die of thine illness, but come to a violent death," puts into the words a meaning which they do not possess. For even if Benhadad did not die of his illness, he did not recover from it.

Howbeit - Here is no contradiction: for the first words contain an answer to Benhadad's question, shall I recover? To which the answer is, thou mayest, notwithstanding thy disease, which is not mortal. The latter words contain the prophet's addition to that answer, which is, that he should die, not by the power of his disease, but by some other cause.