"The sons of God saw that the daughters of men were fair; and they took wives for themselves from those who were pleasing to them."
Who were the sons of God that they should look upon the daughters of men? It seems as if this sentence is saying that they were not men. Then who were they?
Quite a lot could be interpreted from that sentence.
I seem to remember similar stories from Greece before the flood, with the Titans and Gods warring. Where are those histories written?
I recently heard the explanation that makes the most sense to me by a theologian (I think it was Dr. R. C. Sproul)
He demonstrated they were not angels. He said the daughters of men were descendants of Cain while the sons of God were not. The mixture of Cain's nature with the other descendants was the precursor to the need for the flood.
I found his explanation fascinating and need to reflect on it more.
This is also a theme in the apocryphal Book of Enoch: "6:1 And it came to pass when the children of men had multiplied that in those days were born unto 2 them beautiful and comely daughters. And the angels, the children of the heaven, saw and lusted after them, and said to one another: 'Come, let us choose us wives from among the children of men 3 and beget us children.'" http://www.world-mysteries.com/awr_1_10.htm
There's some wild stuff in there.