John Calvin Commentary Genesis 6:2

"that the sons of God saw the daughters of men that they were fair; and they took them wives of all that they chose." — Genesis 6:2 (ASV)

That they were fair. Moses does not consider it condemnable that attention was paid to beauty in choosing wives, but rather that mere lust ruled. For marriage is too sacred for men to be led to it by the lust of the eyes. This union is inseparable, comprising all parts of life, as we have seen before, that the woman was created to be a helper for the man.

Therefore, our appetite becomes brutal when we are so enthralled by the charms of beauty that the most important things are not taken into account. Moses more clearly describes the violent impulsiveness of their lust when he says that they took wives of all that they chose. By this, he signifies that the sons of God did not make their choice from those who possessed necessary qualities, but wandered without discrimination, rushing onward according to their lust.

We are taught, however, by these words, that temperance should be practiced in holy marriage, and that its desecration is no small crime before God. For it is not fornication that is condemned here in the sons of the saints, but the excessive indulgence of freedom in choosing wives for themselves.

And truly, it is inevitable that, in the course of time, the sons of God would degenerate when they thus yoked themselves with unbelievers. This was the ultimate strategy of Balaam; that when the power of cursing was taken from him, he commanded women to be secretly sent by the Midianites, who might seduce the people of God to impious apostasy.

Thus, concerning the sons of the patriarchs whom Moses is now discussing, forgetting the grace that had been divinely given to them was, in itself, a serious evil, especially as they formed unlawful marriages according to their own desire. A still worse consequence followed when, by mixing with the wicked, they desecrated God's worship and fell away from the faith—a corruption that almost always tends to follow the former evil.