In summary, there are four common interpretations of the identity of the “sons of God” of Genesis 6:1-4. The first view was that the sons of God were polygamous human rulers; the second was that the term “sons of God” merely refers, poetically, to regular men marrying regular women; the third view was that the sons of God were the godly male descendents of Seth, and the daughters of men were the wicked female descendents of Cain. The fourth view was that the sons of God were fallen angels, who left their proper domain and natural function to cohabit with human women.
The first three positions are inconsistent at points, leave questions unanswered, and must equivocate on the use of the terms “man” and “sons of God.” The fourth view, that the sons of God were fallen angels, makes the most sense of the distinction between “man” in verse one, and the sons of God in verse two. It is the historical rabbinic view, as well as the view of the early church fathers. The strongest argument for the angel view, however, is that it affirms the established meaning of the phrase “sons of God” as referring explicitly to angelic beings.
This view is the most historically traditional, logically consistent, and exegetically faithful position. Even if it seems strange, or in certain areas is difficult to make sense of, the exegetical weight of letting the Word speak for itself drives the serious student of the Bible to the conclusion that Genesis six is referring to fallen angels who cohabited with human women.
Please don’t take my word for it though. I understand this is a terribly difficult passage. I urge you to continue to consider the options, and study the issues further. As I said earlier, there are numerous other issues relating to this passage which I could not get into, as well as areas that you could delve deeper into. To help you get started with looking into the matter further, here is a list of resources that could be very helpful in this pursuit. I hope you find them helpful!
Ron Bigalke. “Who Were the ‘Sons of God’ in Genesis 6?”
Tim Chaffey. “Battle Over the Nephilim.“Answers in Genesis. 2012.
Gene Cunningham. Genesis Series (specifically the last ~30 minutes of #10). 2003.
Bob Deffinbaugh. “The Sons of God and the Daughters of Men.” Bible.org.
Fred Dickason. Angels, Elect and Evil. Chicago: Moody Press, 1975.
David S. Dockery (editor). Holman Concise Bible Commentary. Nashville: Broadman & Holman Publishers, 1998.
Millard J. Erickson. Christian Theology. Grand Rapids: Baker Academic, 2013.
Drue Freeman. The Angelic Conflict: The Missing Link. Trinity Bible Church of OKC, 2014.
Norman Geisler. Systematic Theology. Minneapolis: Bethany House, 2002.
Wayne Grudem. Systematic Theology: An Introduction to Biblical Doctrine. Grand Rapids: Zondervan, 1994.
Victor P. Hamilton. The Book of Genesis. Grand Rapids: W.B. Eerdmans, 1990.
David Jeremiah. What the Bible Says About Angels: Powerful Guardians, a Mysterious Presence, God’s Messengers. Sisters: Multnomah Books, 1996.
Derek Kidner. Genesis: An Introduction and Commentary. Leicester: Inter-Varsity Press, 1967.
Alex Konya. Demons: A Biblically Based Perspective. Schaumburg: Regular Baptist Press, 1990.
John MacArthur. 1 Peter. Chicago: Moody Publishers, 2004.
John MacArthur. Christians and Demons. Panorama City: Word of Grace.
John MacArthur. Demonic Invasion. Grace Community Church. 2001.
Kenneth A. Matthews. “Genesis 1–11.” In The New American Commentary, edited by David S. Dockery. Nashville: Broadman & Holman, 1991.
Eugene H. Merrill, Mark F. Rooker, and Michael A. Grisanti. The World and the Word: An Introduction to the Old Testament. Nashville: B&H Academic, 2011.
Robert A. Morey. Death and the Afterlife. Minneapolis: Bethany House, 1984.
Michael Oppenheimer. “The Sons of God in Genesis 6.” Let Us Reason. 2013.
E.H. Plumptre. The Spirits in Prison and Other Studies on the Life After Death. London: Isbister, 1898.
Allen P. Ross. “Genesis.” In The Bible Knowledge Commentary: OT, edited by John F. Walvoord and Roy B. Zuck. Wheaton: Victor Books, 1983.
John H. Sailhamer. “Genesis.” In The Expositor’s Bible Commentary, edited by Tremper Longman III and David E. Garland. Grand Rapids: Zondervan, 2006.
Michael G. Wechsler. “Genesis.” In The Moody Bible Commentary, edited by Michael Rydelnik and Michael Vanlaningham. Chicago: Moody Publishers, 2014.
Charles R. Swindoll. Understanding Christian Theology. Nashville: Thomas Nelson Publishers, 2003.
“Who/What Were the Nephilim?” GotQuestions.org.
“Who Were the Sons of God and Daughters of Men in Genesis 6:1-4?” GotQuestions.org.
“Why Did God Also Destroy Animals in the Flood (Genesis 6-8)?” GotQuestions.org.