That the sons of God saw the daughters of men that they were fair; and they took them wives of all which they chose.
The "sons of God" are angels; the same "sons of God" mentioned in Job 1:6, when the sons of God came to present themselves before the LORD; the same "sons of God" mentioned in Job 38:7 that shouted for joy when God laid the cornerstone of the earth's foundation; the same "sons of God" mentioned in 1 John 3:1 & 2 that states:
Behold, what manner of love the Father hath bestowed upon us, that we should be called the sons of God: therefore the world knoweth us not, because it knew him not. Beloved, now are we the sons of God, and it doth not yet appear what we shall be: but we know that, when he shall appear, we shall be like him; for we shall see him as he is.In the Old Testament, the sons of God were angels. In the New Testament, Jesus gives humans "the power to become sons of God" (John 1:12). Today, the sons of God are all that are led by the Spirit of God (Romans 8:14).