Archie T. Wright has an article up on Bible & Interpretation for April 2015 entitled “The Origin of Evil Spirits in Early Jewish Literature“.
In the article, Archie Wright explains the link made between giants and evil spirits/demons in the Book of Watchers (1 Enoch 1-36):
the Fallen Watcher Angels in 1 Enoch have sexual relations with human women and produce what are described as giant offspring. These offspring begin to literally eat the humans out of house and home. Once they have eaten all the food that humans produce, they turn on the humans and begin to devour them; it is then that the call goes up to heaven for God to deliver humanity from the giants. These giants are considered a hybrid offspring, they are part human and also part heavenly being (angel); although the percentage of division (e.g. 50/50) between the two is unclear. The result of the call to heaven by the oppressed humans brings about the destruction of the physical giants by the Archangels Raphael, Michael, Sariel, and Gabriel. The death of the ‘giants’ is brought about by the Flood event in Genesis, which, at the same time, cleanses the earth of the blood shed by the giants and also eliminates corrupt humanity. However, the hybrid spirits of the physical giants survive the flood and are identified in 1 Enoch, and other early Jewish texts, as evil spirits (or demons). The fathers of the giants, the Watcher angels, are locked in a deep pit identified as Tartarus and are bound there with chains and covered with rocks, thus the image you see in the movie “Noah” of the giant beings who seem to be assisting Noah in various aspects of the Flood episode. The Watchers will be held there until the Day of Judgment – there is no notion in 1 Enoch that the evil spirits are fallen angels, rather the spirits of the giant offspring become the evil spirits or demons of the age.
The article coincides with the revised edition of Archie Wright’s book, The Origin of Evil Spirits: The Reception of Genesis 6:1-4 in Early Jewish Literature (Fortress Press, 1 April 2015). The original edition was a fine read on the subject, so I am sure the revised edition will be very good too.
h/t: Jim Davila