In order to explain the giants found in Genesis 6:4, "There were giants in earth in those days;", some Christians have interpreted the phrase "sons of God" from verse 2 to be fallen angels, or demons that mated with human females and created an offspring called giants or Nephilim. I don't believe that this definition of the sons of God is biblically accurate. I believe that the sons of God are believers from the godly line of Seth and the daughters of men are unbelievers. Samuel E. Pierce (1746-1829) addresses this issue in An Exposition of the Epistle of I John [ISBN 1-888514-01-9] when he defines the two sorts of people in our world as seen in 1 John 3:10 (pp. 399-400):
"I am in proceeding with the subjects before me, 1. To show, that there are two sorts of persons, or people, in our world: one are the children of God, the other are the children of the devil. The original terms of distinction were, the seed of the woman, and the seed of the serpent. "I will put enmity between thee and the woman, and between thy seed and her seed; it shall bruise thy head, and thou shalt bruise his heel," Gen. iii. 15.
Adam is called the son of God . Luke iii. 38. It is said of Seth, he had a son born unto him, whom he called Enos. It is added, then began men to call upon the name of the LORD. In the margin it is, or, to call themselves by the name of the LORD. Gen. iv. 26. And in the 6th chapter of Genesis, those who were professors of Christ are distinguished from the serpent's seed, by this title, the sons of God. And by their intermarriages with the Cainites, brought on that universal corruption of men, and the worship of God, as brought the deluge of waters upon the world of the ungodly. When that catastrophe was finished, and the earth renovated, there was the same distinction of the two distinct seeds found upon the earth. They were so distinguished, the one from the other, they could not be blended; there was no uniting so as to become one; it was wholly impossible; they were distinguishable even by their actions, and by their motives from whence they acted; as also the end to which their actions tended. This is the subject on the which the apostle is not treating. He viewed it to be of importance, then; it must be of the same importance now. The title of the children of God, is of vast importance: it is delightful; it is refreshing; it is encouraging; it is strengthening and serves to be very invigorating to the mind."
Mr. Pierce is obviously not under the impression that the "sons of God" are fallen angels.
"In this the children of God are manifest, and the children of the devil: whosoever doeth not righteousness is not of God, neither he that loveth not his brother," (1 John 3:10).