John Calvin Commentary Genesis 26:28

"And they said, We saw plainly that Jehovah was with thee. And we said, Let there now be an oath betwixt us, even betwixt us and thee, and let us make a covenant with thee," — Genesis 26:28 (ASV)

We saw certainly that the Lord was with thee. By this argument they prove that they desired an agreement with Isaac, not deceitfully, but in good faith, because they acknowledge God's favor toward him. For it was necessary to clear themselves of this suspicion, since they now approached so courteously one whom they had previously opposed unreasonably.

This confession of theirs, however, contains very useful instruction. When unbelievers call someone whose affairs all go well and prosper "the blessed of the Lord," they testify that God is the author of all good things, and that all prosperity flows from him alone. Therefore, our ingratitude is exceedingly shameful if, when God is kind to us, we overlook his benefits.

Again, unbelievers consider the friendship of someone God favors as desirable for themselves, recognizing that there is no better or holier recommendation than God's love. Therefore, those are perversely blind who not only neglect those whom God declares to be dear to him, but also wickedly harass them.

The Lord proclaims himself ready to take vengeance on anyone who might injure those whom he protects. Yet most people, unmoved by this most terrible warning, still wickedly oppress the good and the innocent. Here, however, we see that natural understanding dictated to unbelievers what we scarcely believe even when spoken by God himself.

Still, it is surprising that they would be afraid of a harmless man and would require an oath from him that he would not harm them. They should have concluded from the favor God had shown him that he was a righteous man and therefore posed no danger. Yet, because they judge him based on their own character and behavior, they also distrust his integrity.

Such disturbance commonly troubles unbelievers, so that they are inconsistent. Or at least they waver and are torn between conflicting feelings, and have nothing settled and consistent. For those principles of right judgment, which arise in their hearts, are soon stifled by corrupt desires. Thus it happens that what they rightly conceive vanishes, or is at least corrupted and does not produce good fruit.