John Calvin Commentary Genesis 26:10

"And Abimelech said, What is this thou hast done unto us? One of the people might easily have lain with thy wife, and thou wouldest have brought guiltiness upon us." — Genesis 26:10 (ASV)

What is this thou hast done unto us? The Lord does not chastise Isaac as he deserved, perhaps because he was not so fully endowed with patience as his father was; and, therefore, so that the seizing of his wife would not dishearten him, God mercifully prevents it. Yet, so that the censure might produce deeper shame, God makes a heathen his master and his reprover.

We may add that Abimelech chides his folly, not so much with the intention of injuring him as of rebuking him. However, it ought to have deeply wounded the mind of the holy man when he perceived that his offense was liable to the judgment even of the blind. Therefore, let us remember that we must walk in the light which God has kindled for us, lest even unbelievers, who are wrapped in the darkness of ignorance, should reprove our stupor.

And certainly, when we neglect to obey the voice of God, we deserve to be sent to oxen and asses for instruction. Truly, Abimelech does not investigate or prosecute the whole offense of Isaac but only alludes to one part of it. Yet Isaac, when so gently admonished by a single word, ought to have condemned himself, seeing that, instead of entrusting himself and his wife to God, who had promised to be the guardian of them both, he had resorted, through his own unbelief, to an illicit remedy.

For faith has this property, that it confines us within divinely prescribed bounds, so that we attempt nothing except with God’s authority or permission. From this it follows that Isaac’s faith wavered when he swerved from his duty as a husband. Besides, we gather from the words of Abimelech that all nations have the conviction impressed upon their minds that the violation of holy matrimony is a crime worthy of divine vengeance, and consequently, they have a dread of the judgment of God.

For although the minds of men are darkened with dense clouds, so that they are frequently deceived, yet God has caused some power of discrimination between right and wrong to remain, so that each person should carry their own condemnation, and that all should be without excuse. If, then, God summons even unbelievers to His tribunal and does not allow them to escape just condemnation, how horrible is the punishment that awaits us if we endeavor, by our own wickedness, to obliterate that knowledge which God has engraved on our consciences?