Micaiah, as a true prophet of Yahweh, of course rejected the counsel offered him, which he felt to be at once wicked and foolish. Compare also the resolution of Balaam, marginal reference.

And Micaiah said, as the Lord liveth,.... He swore by the living God, for the confirmation of what he was about to say:
what the Lord saith unto me, that will I speak; truly and faithfully, keeping nothing back, nor adding anything, whether it be good or evil, pleasing or displeasing; it looks as if as yet he had no instruction from the Lord what to say, and yet the vision he later declares seems to have been had by him before, 1-Kings 22:17.

what the Lord saith unto me, that will I speak--On the way the messenger who conducted [Micaiah] to the royal presence informed him of the tenor of the prophecies already given and recommended him to agree with the rest, no doubt from the kindly motive of seeing him released from imprisonment. But Micaiah, inflexibly faithful to his divine mission as a prophet, announced his purpose to proclaim honestly whatever God should bid him. On being asked by the king, "Shall I go against Ramoth-gilead, or shall I forbear?" the prophet gave precisely the same answer as the previous oracles that had been consulted; but it must have been given in a sarcastic tone and in ironical mockery of their way of speaking. Being solemnly urged to give a serious and truthful answer, Micaiah then declared the visionary scene the Spirit had revealed to him;--

Said - What answer God shall put in to my mouth. Bravely resolved! And as became one who had an eye to a greater king than either of these.