When the folks who wrote the older testament scriptures, the Jews, were the only interpreters of those scriptures the explanation of Genesis 6:1-4 was as follows, the heavenly sons of God, the Watchers (a class of angels) lusted after the daughters of mankind and conspired to break God's law, leave their assigned abode in heaven, take human wives, defile themselves by sexual relations with women and to beget children who turned out to be gigantic. That was the unified Semitic view from the period of 2nd-Temple Judaism.
This can be confirmed by anyone by picking up a copy of "
The Dead Sea Scrolls Study Edition", by Florentino Garcia Martinez, Eibert J. C. Tigchelaar, and Florentino Garcia Martinez. This is THE MOST exhaustive collection of the non-Hebrew-Bible Dead Sea Scrolls that is available.
If one begins at the beginning of those volumes and proceeds to read through these fragments from hundreds of Jewish religious documents from about the time of Christ, one will get a profound sense that the preoccupation with the Watcher/Giant saga among Jewish writers during and before the time of Christ, borders on obsession. In addition to all of the books of the Hebrew Bible, the Dead Sea Scrolls include many story fragments from the lives of Lamech, Noah, Enoch, Methuselah and the rest as well as numerous accounts of the history of the Nephilim, the gigantic offspring of the Watchers.
One is stricken with the sheer lack of controversy among these writers on this point. To date, I have yet to find even one example from the period of 2nd-Temple Judaism wherein some rabbi or religious writer has a controversy with the Watcher/Nephilim thesis, though controversy abounds on other subjects.
There is evidence that this view prevailed among New Testament writers in the New Testament books as well, but that is perhaps better addressed in another post or thread.
Certainly the idea that angels could even interbreed with human women seems repugnant to our modern sensibilities and apparently it was also for the leaders of the Church from the fourth century forward. I would like to propose however, this offense to our sensibilities has more to do with Greek assumptions about the nature of angels than it does with any scriptural basis.
I have detected several areas in which the Church's ideas concerning angels are at major variance with the dominant view during the time of Christ; here are a few:
1. Angelic substantiality
Per the prevailing ideas about angels among Christians of all stripes, angels are viewed as spirits, without materiality. Western ideas about the essential differences between human carnality and angelic spirituality make the idea of angelic/human copulation seem impossible. In the Semitic writings from 2nd-Temple Judaism no such problem can be detected. There is a consensus among Semitic writers from the period that angelic spirituality as well as angelic carnality were both simultaneously real, and not mutually exclusive. The writer of the Book of Jubilees even speaks of angels having been created in a circumcised state from the beginning.
2. Angelic peccability
Per the prevailing ideas of Christians there seems to be somewhat a consensus that somewhere in very ancient times there occurred a rebellion among the members of the heavenly angelic hosts. Whatever the reasons for this rebellion, the result was certain angels aligned themselves with Lucifer, rebelled against God and thus sinning, fell. A seemingly assumed corollary to this view is the idea commonly held among Christians that those angels who did not fall, stood the test and are thenceforth immune to further testing, temptation and the possibility of sinning. No such assumptions can be detected amongst Jewish writers from the period of 2nd-Temple Judaism. Not only did angels fall during the time of Jared the father of Enoch, but previous fallings had occurred and future fallings are predicted.
For me, what Jewish writers from the time of Christ believed about this point holds more persuasive weight than when it was controverted by Christendom centuries later. To the Jews were given the lively oracles of God. The oracles were in a language whose meanings would have been more immediate to them than to us. The Jews lived closer to the times of the actual composition of those writings and thus were more likely to be the inheritors of original traditions related to their exposition, interpretation and understanding.