John Calvin Commentary Genesis 20:6

"And God said unto him in the dream, Yea, I know that in the integrity of thy heart thou has done this, and I also withheld thee from sinning against me. Therefore suffered I thee not to touch her." — Genesis 20:6 (ASV)

Yea, I know that you did this in the integrity of your heart. We infer from this answer of God (as I have lately remarked) that Abimelech did not testify falsely concerning his own integrity. Yet, while God allows that his excuse is true, He nevertheless chastises him.

Let us therefore learn that even those who are pure, according to human judgment, are not entirely free from blame. For no error can be considered so excusable as to be without some deteriorating admixture. Therefore, it is not for anyone to absolve himself by his own judgment; rather, let us learn to bring all our conduct to the standard of God.

For Solomon does not say in vain that the ways of men seem right to themselves,
but the Lord ponders the hearts, (Proverbs 21:2).

But if even those who are unconscious of any evil in themselves do not escape censure, what will be our condition if we are held inwardly bound by our own conscience?

I also withheld you. This declaration implies that God had regard not only for Abraham but also for the king. For because he had no intention of defiling another man’s wife, God had compassion on him.

And it frequently happens that the Spirit restrains, by His bridle, those who are gliding into error; just as, on the other hand, He drives those headlong, by infatuations and a spirit of stupor, who, with depraved affections and lusts, knowingly transgress. And as God brought to the pagan king, who had not been guilty of deliberate wickedness, a timely remedy so that his guilt should not be increased, so He proves Himself daily to be the faithful guardian of His own people, to prevent them from rushing forward from lighter faults to desperate crimes.