The Nephilim were on the earth both in those days and afterward, when the sons of God came to the daughters of mankind, who bore children to them. They were the powerful men of old, the famous men.
Genesis 6:4 HCSB
The phrase “Sons of God” can be applied to two groups of God’s creatures. Angels (Job 1:6) and believers in Jesus Christ (Galatians 3:26). I believe that the “sons of God” mentioned here are referring to angels. I will show you why. In Jude 1:6-7, it says, “6 and He has kept, with eternal chains in darkness for the judgment of the great day, the angels who did not keep their own position but deserted their proper dwelling. 7 In the same way, Sodom and Gomorrah and the cities around them committed sexual immorality and practiced perversions, just as angels did, and serve as an example by undergoing the punishment of eternal fire.”
The connection of Genesis 6 and Jude 1 is that the sons of God, angels, perverted themselves with earthly women by having intercourse with them. We know that God didn’t create angels with men’s genitalia. Most likely, they either possessed a human body, or they had the power to produce men’s private part.
The “Nephilim” did not come from the “sons of God” as some think they did. The reason for this is the structure of the verse. The passage says that the Nephilim were on the earth before and after the incident of the fallen angels giving themselves to earthly women for marriage. The Nephilims were giants, but not because of the angel’s offspring. The angel’s offsprings were famous because they exhibited superhuman powers.
Spiritual Minefield 