Now it came about, when men began to multiply on the face of the land, and daughters were born to them, 2at the sons of God saw that the daughters of men were beautiful; and they took wives for themselves, whomever they chose. 3Then the Lord said, ? My Spirit shall not strive with man forever, because he also is flesh; nevertheless his days shall be one hundred and twenty years.? 4The Nephilim were on the earth in those days, and also afterward, when the sons of God came in to the daughters of men, and they bore children to them. Those were the mighty men who were of old, men of renown," (Gen. 6:1-4, NASB).
There is debate over exactly who the Nephilim are in Gen. 6. Some people believe that the Nephilim are the offspring of sexual relations between fallen angels and human women. Jude 6 is often referenced as additional support when addressing the angelic realm who "...did not keep their own domain, but abandoned their proper abode..." (Jude 6). Others believe the Nephilim were giants (Nephilim means giants), men of great physical stature. Of course, this also is believed by some people who suspect that the offspring of the fallen angels and the women were those giants which they say would explain their large size. But this is conjecture. Still others hold that the Nephilim are the descendents of Seth.1
According to Harper's Bible Dictionary, the Nephilim are "people of the pre-Flood generation, the offspring of daughters of men and divine beings (Gen. 6:1-4). Their generation and their conduct seem to have provoked the Flood as punishment (Gen. 6:5 - 8:22). In Num. 13:33 the Israelite spies describe the inhabitants of Hebron as Nephilim, so large and powerful that ?we seemed like grasshoppers.? The name could mean ?fallen ones? and allude to stories in related cultures of rebellious giants defeated by the gods in olden times (cf. Isaiah 14:12)."2 Of course, a problem with this view is how did the Nephilim survive the flood? We see a post-flood account of them in Num. 13:33, "There also we saw the Nephilim (the sons of Anak are part of the Nephilim); and we became like grasshoppers in our own sight, and so we were in their sight.?
The range of options is varied. Consider this:
"Many have suggested that the sons of God were the godly line of Seth and the daughters of men were the Cainites. But this does not do justice to the terminology or the context. Others view the ?sons of God? as angels (as in Job 1:6), who cohabited with women on earth. This, however, conflicts with Matt. 22:30."3
"The term [Nephilim, Giants] in Hebrew implies not so much the idea of great stature as of reckless ferocity, impious and daring characters, who spread devastation and carnage far and wide."4
"The improper mating of heavenly beings and earthly women is an attack on the boundaries that are meant to separate the heavenly and earthly realms. It thus threatens the integrity of creation as God intended it."5