The Book of Enoch

Enoch was the seventh from Adam and the great-grandfather of Noah (Genesis 5:19, 29). Among the Dead Sea Scrolls discovered in the caves of Qumran was the 'book of Enoch' which confirmed its antiquity and authenticity in history, as well as its popularity among the early Jews and attested even by one New Testament writer (Jude 1:14). 

This book made reference to the fallen angels mentioned in the Genesis account and painted a picture of how the world looked like before the deluge. It tells how the eyes of this patriarch was opened by God to see heavenly visions and future cataclysmic events that shall befall mankind. At the beginning of the book is a rather intriguing statement:

The words of Enoch, wherewith he blessed the elect and righteous, who will be living in the day of tribulation, when all the wicked and godless are to be removed.

Enoch a righteous man whose eyes were opened by God, saw the vision of the Holy One in the heavens, which the angels showed me, and from them I heard and from them I understood as I saw, not for this generation, but for a remote one which is to come.

The 'day of tribulation' might not have referred to the coming deluge in Noah's day, but to a 'remote' (distant) generation that is to come. Of course, Enoch could very well be hinting at this particular generation we're living in.

Notably, Enoch clearly mentioned the existence of angels. Some of these angels—the fallen ones—abducted beautiful mortal women to produce offspring of their own, hybrids that resulted from the union of angels and humans.

These demi-gods possessed not only great strength but physical stature and were given the title 'Nephilim' which means 'giants' in Hebrew. This is consistent with the narrative of the Bible in Genesis chapter six.

The book of Enoch went further and described how these giant hybrids ruled the earth in ancient times. They exhausted the earth's food resources and when humans were unable to supply their insatiable appetite, these giants turned on them and consumed human flesh for sustenance instead. Nephilim's inclination towards lusts and destruction filled the earth with chaos, immorality and violence.

Some will object to this line of thought and insist that angels do not or are not capable of sexual acts based on Jesus' answer to the Sadducees, who questioned the reality of resurrection and the spiritual world:

Matthew 22:29-30
You are in error because you do not know the Scriptures nor the power of God. For in the resurrection people will neither marry nor be given in marriage, but they will be like the angels in heaven.

Such reasoning betrays a lack of understanding on the nature of angels and the purpose they were created. As far as angels are concerned, there is no necessity for procreation since they are spiritual beings, created to serve God and the heirs of salvation. But the human race is a completely different story altogether because they need to reproduce to continue their short, earthly existence. As such, mankind is created male and female whereas angels are singularly male.

It is therefore not a stretch on the imagination that fallen angels should take a fancy on mortal women and commit the forbidden act which resulted in their premature punishment:

Jude 1:6-7
And the angels who kept not their first estate (position), but left their own habitation (place), God has reserved in everlasting chains under darkness unto the judgment of the great Day—even as Sodom and Gomorrah and the cities around them, in the same way giving themselves over to fornication (consensual sexual intercourse) and going after strange flesh (unnatural union), are set forth as an example, suffering the vengeance of eternal fire.

These fallen angels not only intruded into forbidden territory themselves, they also led mankind astray with all sorts of dark occultic knowledge that turned their hearts away from God to the worship of the heavenly hosts and the practice of witchcrafts —detestable things which God had strictly forbidden. They also imparted the ability and skills to make weapons which resulted in ceaseless bloodshed and sufferings. The fallen angels brought their knowledge to mankind, and with it unimaginable disasters and endless miseries. No wonder the Bible solemnly states:

Genesis 6:11-12
The earth also was corrupt before God and violence filled the lands… for all flesh had corrupted his way upon the earth.

The only option left was divine judgment. The whole earth must be cleansed and rid of all the filth and evil, and the means would be through a worldwide flood. As for these fallen angels, they too would be imprisoned ahead of their time and to await their final judgment (Jude 1:6).