Reversing Hermon by Dr. Michael S. Heiser:
Spiritual Warfare is a dangerous topic, and there are more than fifty passages in the Bible warning against deception, worshipping angels, and other false forms of worship. If we venture into this realm, we ought to first be armed with very precise Biblical knowledge about what the Bible tells us about the nature of good and evil. While often unsettling and even seemingly contradictory to modern worldviews, Reversing Hermon provides us with the Scripturally accurate account of the origins and nature of evil as understood in the context of first-century Christians.
Genesis 6:1-4 describes how the sons of God took the daughters of men as wives and gave birth to giants known as Nephilim. Heiser examines how this passage has been understood throughout Christian history and then references 2 Peter 2:1-10 and Jude 5-7 to illustrate his own perspective.
Heiser's discussion brings up the pseudepigraphal text of 1 Enoch. This account can be very difficult for the modern reader to accept, yet it was the accepted view of the nature of good and evil around the time of Christ and is even quoted in Jude 14-15.
Reversing Hermon makes the simple argument that if we are to understand the New Testament, then we must understand the cultural context in which it was written. In 1 Enoch, supernatural beings - Watchers - leave their heaven and bring secret knowledge to humankind. They also have sexual relations with human women and produce the Nephilim. When the Nephilim died, their spirits became what we would call demons
Spiritual Warfare is dangerous. The first step is to carefully read the Bible in the context of the time it was written (not project our modern understandings into the texts). Reversing Hermon is the ideal guide for this process.