Genesis 6:1-4 has perplexed readers for centuries: “When man began to multiply on the face of the land and daughters were born to them, the sons of God saw that the daughters of man were attractive. And they took as their wives any they chose. Then the LORD said, ‘My Spirit shall not abide in man forever, for he is flesh: his days shall be 120 years.’ The Nephilim were on the earth in those days, and also afterward, when the sons of God came in to the daughters of man and they bore children to them. These were the mighty men who were of old, the men of renown.” Who are these sons of God? Who are the Nephilim?
The phrase “sons of God” is only used in the Old Testament to refer to angels (Deut 32:8; Job 1:6; 2:1; 38:7; Ps 29:1). Jude 1:6-7 gives us an interpretive lens to help us better understand this passage: “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 – just as Sodom and Gomorrah and the surrounding cities, which likewise indulged in sexual immorality and pursued unnatural desire, serve as an example by undergoing a punishment of eternal fire.” The unnatural union of fallen angels with man in Genesis 6 is analogous to the unnatural sexual immorality of Sodom and Gomorrah. The key phrase in Jude that alludes to Genesis 6:1-4 is “which likewise” that draws a comparison between the unnatural desires of these angels in the verse six with those of Sodom and Gomorrah. But the men of those cities did not know that the men they lusted after were angels in disguise. They were not desiring after sex with angels, but with other men.
But how could fallen angels have sexual relations with human woman? While angels are not flesh and blood, they can transform themselves to resemble fleshly creatures as Satan transformed himself into a serpent (Rom 16:20; 2 Cor 11:3; Rev 12:9). The word Nephilim literally means “giants” because the offspring of this union were unnatural. This is one of the reasons why God had to send a worldwide flood to destroy these creatures. Sexual immorality is demonic because the demons envy man’s ability to engage in sexual relations which are forbidden to them. Those who tried to engage in it were condemned to hell immediately while the other demons who did not were spared until the time of Revelation 20:10. For us to engage in sexual relationships which are forbidden to us is to imitate them. Hence, the demons try to destroy sex by perverting it because it is a picture of the union of Christ and his bride, a salvation which they do not participate in and are envious of.