In Genesis 6:1-4, there is a statement that has caused a lot of speculation: “And it came to pass when men began to multiply on the face of the earth, and daughters were born unto them, that the sons of God saw the daughters of men that they were fair; and they took them wives of all which they chose … There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare children to them, the same became mighty men which were of old …”
Some have guessed that these were angels or heavenly beings of some sort. The theory goes that these beings lusted for and ultimately mated with human women. The “mighty men” that resulted from these unions are held up as proof that something “extra-earthly” had occurred.
There are two major problems with this view. First, this view ascribes human sexual desire to heavenly beings, which is mere speculation (cp. Matthew 22:30). Second, this view diminishes the uniqueness of the virgin birth of Jesus. His case stands alone as one in which a child was born by some means other than by natural conception.
Genesis 4:26 says, “… then began men to call upon the name of the Lord.” In the beginning, some men chose to follow God. Those who “called upon the name of the Lord” were known as the “sons of God.” As time went on, even these men began to be corrupt (including their marriages to wicked mates). Finally, they were so full of sin and corruption that “it repented the Lord that he had made man” (Genesis 6:6-7).