2 And Abraham said of Sarah his wife, She is my sister: and Abimelech king of Gerar sent, and took Sarah.
3 But God came to Abimelech in a dream by night, and said to him, Behold, thou art but a dead man, for the woman which thou hast taken; for she is a man’s wife.
4 But Abimelech had not come near her: and he said, Lord, wilt thou slay also a righteous nation?
5 Said he not unto me, She is my sister? and she, even she herself said, He is my brother: in the integrity of my heart and innocency of my hands have I done this.
6 And God said unto him in a dream, Yea, I know that thou didst this in the integrity of thy heart; for I also withheld thee from sinning against me: therefore suffered I thee not to touch her.
God came to Abimelech with a strong sentence: “thou art but a dead man!” But when Abimelech professed innocence of any wrong God admitted that he already knew this to be the case. He was actually only warning Abimelech from destruction.
But why did God approach the matter in this way? Why start by pronouncing a punishment for a crime that Abimelech was innocent of? I can’t know for sure, but one possibility might be that God was helping Abimelech to evaluate the state of his own heart.
Being put on trial is often thought of as an unpleasant thing, but sometimes it can be a cleansing, justifying experience. By taking a close inventory of all their actions and motivations, the innocent are relieved to find that their heart really is pure, more so than they even realized. They can look anyone in the eye and honestly testify of their own worthiness. It could be that this experience was what God sought for Abimelech, even if it took a little fire to get him there.