There is an ancient interpretation of this which we believe to be quite ludicrous, that the reference here to the ‘sons of God’ refers to angels, wicked angels, fallen angels, who came down to earth and had intercourse with women, and thereby produced a particularly evil generation. That has been taught from many years back among the fanciful interpreters of the Jews, and, indeed, was taught by some of the church fathers. But it is an absurd interpretation that does not fit the text, the account in chapter 5 and chapter 6 at all. Indeed, Calvin was very harsh against it. He called it an ancient figment, and he said it was adequately refuted by its own absurdity. He called it crass and gross, and used all kinds of adjectives. It made him rather angry that people could interpret in such a foolish way, and make fables out of the word of God, and the Reformed tradition has generally taken that view.
Even today, some hang onto this interpretation, and they reason that there are three verses in the book of Job where the phrase in the Hebrew, ‘the sons of God’, refers to angels. Yes, but there are verses in other portions of the Old Testament where the sons or children of God clearly refer to the people of God. There are also 6 verses in the New Testament where the phrase ‘sons of God’ indisputably refers to Christians. So, if you were interpreting on the foolish basis of the number of times a phrase is used in a particular context, there would be a majority in favour of the interpretation that the sons of God here in Genesis 6 are in fact the people of God, the godly. This interpretation is refuted by other texts too. The Lord Jesus Christ in Matthew 22 tells us quite clearly that in heaven, there will be no marrying or giving in marriage because we shall be like the angels. They cannot marry; they cannot produce offspring; they cannot be incarnated into the world. They may appear in the world, as they do in the Old Testament, in a human form at the direct bidding and instruction of God, but they cannot of themselves take on a body: they are ministering spirits.
But the context confirms this. We are told what the subject is. The present section begins in Genesis 5:1 – ‘This is the book of the generations of Adam’ – and it runs all the way down to Genesis 6:9 – ‘These are the generations of Noah.’ This is the book which traces the history of human beings, of the pre-flood patriarchs. There is no room, here, for the mythical generation of angels to be introduced; that is quite out of the context, and the storyline of these chapters is the preservation of the promised seed of Messiah, and the great conflict between the church and the world. Whatever then is this? To introduce the myth, nowhere else referred to, of fallen angels have intercourse with women. Well, Calvin quite rightly calls it an absurdity and a figment of a fevered imagination. So we dismiss that quite strongly, so that we can stick to the narrative, which is what really matters.