Eliyahu relates to Ahav's personal fate and the terrible punishment to his dynasty in the aftermath of his sin toward Navot and his vineyard - the culmination of the sinful reign of Ahav. Surprisingly, Ahav rends his clothing, wears a sackcloth and fasts. It appears that God accepts Ahav’s repentance, as He marvels to Eliyahu, “Have you seen that Ahav has submitted before me?”
Was Ahav’s repentance sincere? Does God accept the repentance of a man who led such a sinful life?
God's question expresses wonder at the fact that a person with the status of the King of Israel, who is mired in the depths of terrible sin, can break down and humble himself before God. Even if this is not complete repentance, Ahav's submission demonstrates a person's ability to melt his heart of stone and thereby attain some measure of Divine pardon.
Indeed, there is a dual lesson to be learned from this narrative, regarding the great power people possess to turn back from the depths of sin, and regarding the power of repentance which, even if not complete, has an effect on one's relationship with God, and when sincere, might be accepted even under dire circumstances.