Gen 6:1 .When humankind began to multiply on the face of the earth, and daughters were born to them, 6:2 the sons of God saw that the daughters of humankind were beautiful. Thus they took wives for themselves from any they chose.

Who were these ‘sons of God’?

(a) Angels or demons?

The view of many interpreters, ancient (e.g. Josephus) and modern (e.g. Wenham,) is that these are (fallen) angels, cf. 1 Pet 3:19-20; 2 Pet 2:4; Jude 6.

The noncanonical book 1 Enoch (200 BC) claims that 200 angels from heaven, seeing that humans had unusually beautiful daughters, came down to earth and each took a wife. The women gave birth to giants, who consumed all the food and even devoured people. One version of the LXX (300 BC) supports this view, (translating ‘sons of God’ as ‘angels of God’ in v2), as does Josephus (born 37 BC).

It is true that in Job 1:6,2:1,38:7 ‘sons of God’ does stand for ‘angels’. However, our Lord explicitly stated that angels do not marry, Mk 12:25. Moreover, if the sin was angelic, why was it that the humans were condemned and punished, Gen 6:5?

Against the view that ‘sons of God’ always refers to angels, see Deut 14:1. Additionally, we may note that the equivalent Gk phrase in Lk 3:38 refers to a man (Adam), as does a similar phrase (’sons of the Most High’) in Ps 82:6.

But if not angels, maybe they were some other kind of supernatural being?  Drawing on recent research, Heiser (The Bible Unfiltered) argues strenuously for this view.  He points to close parallels between Gen 6:1-4 and Mesopotamian literature.  This literature tells of divine beings names apkallu, who cohabited with human women, producing divine/human offspring who were giants.  The Genesis account sees them as the rivals of God and his people, and deserving of death.  See also this.

Steinmann detects a number of problems with this theory:

(a) It introduces angels into the narrative with little or no prior mention.

(b) Jesus teaches that angels do not marry (Mt 22:29–30 and parallels).

(c) Scripture does not depict angels as having bodies like ours.  It is therefore hard to see them mating with humans.

(d) It is incongruous that God’s judgement should fall on the human race (vv3,5-7) because of what angels did.

(b) Demonised humans?

Waltke thinks that the ‘sons of God’ were demon-controlled human tyrants.

Storms (Deciphering Difficult Texts) adopts this view:

‘Gen. 6 describes the “sin” mentioned in 2 Pt. 2:4 and Jude 6 (and 1 Pt. 3:18–20). Subsequent to their fall from heaven, and as an expression of their moral depravity, an unspecified number of those demons inhabited (took up residence in) human bodies and contracted marriage relationships with the “daughters of men.” Thus we are reading about a case of demonized men entering into marriage with women and contributing greatly to the increase of depravity and corruption in the earth (Gen. 6:5–7). These demons were, at some later time, consigned to permanent imprisonment until the day of final judgment.’

(c) Humans?

Some conservative scholars interpret “sons of God” as a reference to the godly Sethite line (Gen. 5; so Calvin, Mathews, Steinmann and others) or to the nobility (cf. Kline; HSB), whose mixed marriages to the “daughters of men” (female descendants of Cain, or “daughters of men” in a restricted sense as wicked or common people) contributed to a moral decline.

Carol Hill (A Worldview Approach to Science and Scripture):

‘The phrase “the sons of God” refers to the chosen line of Adam, while “the daughters of men” could refer to the population of humans that lived alongside the line of Adam. That would explain why they took these women as wives, and also why the flood account directly follows in Genesis 6. The unbelieving wives from the non-Adamite population were turning their believing husbands away from God and toward wickedness and idol worship. Among the children of these unions were the giants (Nephilim) of Genesis 6:4, who seem to have survived Noah’s flood, as they reappear in Numbers 13:33–still another reason for not interpreting Noah’s flood as globally killing off all the people on planet Earth besides Noah and his family.’

They argue that “myth” is inconsonant with the perspective of the Pentateuch, that “angels” are pure in Genesis and sexless in the Bible as a whole, (Mt 22:30) and that people should not be punished (Gen 6:3) for a sin that is primarily that of angels (v 2).’ (ISBE)

A weakness of this view is the ‘sons of God’ is not used elsewhere in the OT of human rulers.

Conclusion

I think that this third view has most to commend it.