The root cause of such a momentous event as the Great Flood started when the sons of God saw that the daughters of men were beautiful (see Genesis 6:1-2),
In the Coptic Church the sons of God is not gender specific but represents the children of Adam and Eve through their son, Seth, who replaced Abel and was the seed who led to the Lord Jesus Christ. The daughters of men is again not gender specific but represents the children of Adam and Eve through their son Cain who murdered his brother Abel
Genesis 6:4 says, “There were giants 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.” The sons of God were not aliens, angels, or other non-human forms that married daughters of men resulting in a different mingled human race. The Bible states their offspring to be “mighty men” but they were humans, not angels. God said, “My Spirit shall not strive with man forever, for he is indeed flesh” and, “I will destroy man whom I have created from the face of the earth” (Genesis 6:3, 7). If angels were the subject of these verses, they could not be capable of reproducing as mankind does since they are of a different host as mentioned in Chapter 1 and clearly stated in Genesis 1, 6, and 7 regarding the principal of creation each “according to its kind.”
As the sons of God multiplied in numbers, they became less and less aware of their relationship as brothers and sisters to one another and began to view the daughters of men as objects for sexual pleasure. This led men into having multiple wives and ungodly relationships with women. It is no
coincidence that an event as significant as the Great Flood occurred at a time when men’s perception of daughters was not aimed at developing a godly relationship consistent with raising a family but more towards satisfying selfish desires. Sin is not limited to gender and God saw evil in these unlawful physical interactions.