Angels can sometimes cause problems, and this is one of those times.
“Sons of God” is a phrase in the Old Testament unique to angels. Job is the best known citing of them, where there is an early reference to the “Sons of God” coming before the Lord, and “Satan” was with them (Job 1:6 & 2:1), but also in Job 38:7 those same angelic “Sons of God” shouted for joy when God created the world.
The human race grew, and the daughters of Eve were stunning and gorgeous, drawing the attention of angels better known as “Nephilim.” The text is clear on the sexual relationship those angels had with women, and they somehow had power to alter human DNA producing children who became “mighty,” in kind of a weird way.
Unclear is whether before the flood angels could manifest on their own into human form, or if they needed to invade a human host, the bible does not clarify that point, but a chilling phrase is found in v. 4, “The Nephilim were on the earth in those days, and also afterward.”
God declared what took place as evil and wrong.
Jude explained what happened this way, “Angels who did not stay within their own position of authority, but left their proper dwelling, he has kept in eternal chains…until the judgment of the great day,” (Jude 6). Jude 7 clarified the sexual nature of their actions when he said, “…indulged in sexual immorality and pursued unnatural desire,” (Jude 7). Those angels sinned in their actions and in so doing became demons, and God gave them a severe judgment, placing them in eternal chains until the day when they will join Satan at the final judgment.
God’s heart was grieved, the Garden of Eden and the Tree of Life were blocked, human DNA was now corrupt, certain angels showed no restraint, and “every intention of the thoughts of man’s heart was only evil continually.” God decided to shorten the life span of humans, “his days shall be 120 years.” Gone were the days of the first humans allowed to live almost a thousand years.
God concluded the need to redo all creation, humans and animals, their corruption so filthy, a global flood was sent to cleanse the earth.
God rescued the human race through a man named Noah, whose name means “Rest,” and gave him supernatural grace and favor.