Genesis 6:1

1.And it came to pass, when men began to multiply. Moses, having enumerated in order, ten patriarchs, with whom the worship of God remained pure, now relates, that their families also were corrupted. But this narration must be traced to an earlier period than the five hundredth year of Noah. For, in order to make a transition to the history of the deluge, he prefaces it by declaring the whole world to have been so corrupt, that scarcely anything was left to God, out of the widely spread defection. That this may be the more apparent, the principle is to be kept in memory, that the world was then as if divided into two parts; because the family of Seth cherished the pure and lawful worship of Good, from which the rest had fallen. Now, although all mankind had been formed for the worship of God, and therefore sincere religion ought everywhere to have reigned; yet since the greater part had prostituted itself, either to an entire contempt of God, or to depraved superstitions; it was fitting that the small portion which God had adopted, by special privilege, to himself, should remain separate from others. It was, therefore, base ingratitude in the posterity of Seth, to mingle themselves with the children of Cain, and with other profane races; because they voluntarily deprived themselves of the inestimable grace of God. For it was an intolerable profanation, to pervert, and to confound, the order appointed by God. It seems at first sight frivolous, that the sons of God should be so severely condemned, for having chosen for themselves beautiful wives from the daughters of men. But we must know first, that it is not a light crime to violate a distinction established by the Lord; secondly, that for the worshippers of God to be separated from profane nations, was a sacred appointment which ought reverently to have been observed, in order that a Church of God might exist upon earth; thirdly, that the disease was desperate, seeing that men rejected the remedy divinely prescribed for them. In short, Moses points it out as the most extreme disorder; when the sons of the pious, whom God had separated to himself from others, as a peculiar and hidden treasure, became degenerate.

That ancient figment, concerning the intercourse of angels with women, is abundantly refuted by its own absurdity; and it is surprising that learned men should formerly have been fascinated by ravings so gross and prodigious. The opinion also of the Chaldean paraphrase is frigid; namely, that promiscuous marriages between the sons of nobles, and the daughters of plebeians, is condemned. Moses, then, does not distinguish the sons of God from the daughters of men, because they were of dissimilar nature, or of different origin; but because they were the sons of God by adoption, whom he had set apart for himself; while the rest remained in their original condition. Should any one object, that they who had shamefully departed from the faith, and the obedience which God required, were unworthy to be accounted the sons of God; the answer is easy, that the honor is not ascribed to them, but to the grace of God, which had hitherto been conspicuous in their families. For when Scripture speaks of the sons of God, sometimes it has respect to eternal election, which extends only to the lawful heirs; sometimes to external vocations according to which many wolves are within the fold; and thought in fact, they are strangers, yet they obtain the name of sons, until the Lord shall disown them. Yea, even by giving them a title so honorable, Moses reproves their ingratitude, because, leaving their heavenly Father, they prostituted themselves as deserters.