The word "Nephilim" means "fallen ones, giants" and is used in Genesis 6:1-4 to describe the offspring of a sexual union between "the sons of God" and "the daughters of men." This shocking but brief account is so supernatural and strange that people have debated the meaning of the words "sons of God" for years. While elsewhere in the Bible that phrase is used to describe angels, some people have postulated that "sons of God" were from the line of Abel, while the "daughters of men" were the offspring of Cain. This postulation is not supported with Scripture, and so it is wisest to assume that the phrase "sons of God" does indeed mean "angels."
Nephilim - Who or what were they?
Although strange, this scenario is not impossible and is supported by a passage in Jude which refers to the fallen angels (demons) who left their proper place and, like those in Sodom and Gomorrah, pursued unnatural sexual relations. The union of the angelic beings with humans would definitely fall into the category of "unnatural" and it is likely that these are the demons being referred to in Jude.
This unnatural sexual union apparently somehow produced strange offspring, which were described as "heroes of old, men of renown" (Genesis 6:4 NIV). These heroes of old were also called "Nephilim." This name, plus other biblical stories about giants such as Goliath, suggests that these were a race of both very large and very strong men. Hebraic legends in the Book of Enoch and other extra-biblical texts also talk about the Nephilim as a race of giants who were able to do amazing things, but also performed acts of great evil. Their strength and size were most likely the product of demon "DNA" combined with human genes.
What was the motive for creating the Nephilim? The Bible does not tell us. We may speculate that the demons were attempting to pollute or destroy the blood line that would produce the Messiah, Jesus Christ, in order to thwart God's plan for the salvation of humanity. The prophecy is that the Messiah would crush the serpent's head (Genesis 3:15), so it is possible they were also trying to prevent this.
It is also possible that the Nephilim were one of the main reasons for the flood of Noah's time. Just after the Genesis passage about the Nephilim, we find the story of Noah's ark and the flood that destroyed every living thing except those on the ark. God's Word says of the pre-flood earth, "The LORD saw that the wickedness of man was great in the earth, and that every intention of the thoughts of his heart was only evil continually. And the LORD regretted that he had made man on the earth, and it grieved him to his heart. So the LORD said, 'I will blot out man whom I have created from the face of the land, man and animals and creeping things and birds of the heavens, for I am sorry that I have made them'" (Genesis 6:5-7). This would have killed everything on the earth, including the Nephilim, leaving only the unpolluted blood carried by Noah and his offspring (Genesis 6:11-22).
However, we do know that there were Nephilim on the earth also after the flood, as Genesis 6:4 says, "The Nephilim were on the earth in those days, and also afterward." Therefore, we must assume that the demons committed their sin again, sometime after the flood. Apparently it was to a much lesser extent, perhaps (it is theorized) localized in the region of Canaan. When the Israelites went to spy on the land of Canaan, the spies reported back to Moses and the others: "And there we saw the Nephilim (the sons of Anak, who come from the Nephilim), and we seemed to ourselves like grasshoppers, and so we seemed to them" (Numbers 13:33).
It is possible that the spies saw very large people in the land of Canaan and supposed them to be Nephilim, or it is possible that they actually were Nephilim – a new group, created after the flood. Whichever it was, these "giants" were destroyed by the Israelites, with God's help, during their invasion of Canaan (Joshua 11:21-22) and also later (Deuteronomy 3:11; 1 Samuel 17).
Is there anything that prevents demons from making more Nephilim today? From the passage in Jude, we can assume that the angels who committed this sin originally are currently being held in the abyss. Jude verse 6 tells us, "And the angels who did not stay within their own position of authority, but left their proper dwelling, he has kept in eternal chains under gloomy darkness until the judgment of the great day." Not all demons are in this "prison" but only the ones who mated with human females. Assumedly, this was a group that went beyond the others in their commitment to evil. It does not necessarily mean that others could now follow suit, but as with all things, it would have to be allowed by God, and part of the ultimate plan to redeem humanity and glorify Himself.
In Genesis 6:1-4, what were the identities of the sons of God and daughters of men?
What are demons according to the Bible?
When was the fall of Satan, and how did it happen?
Why did God allow the Satan and the demons to sin?
Are all angels male or are some female?
Truth about Angels