And He answered and said to me, and I heard His voice: ‘Fear not, Enoch, thou righteous man and scribe of righteousness: approach hither and hear my voice. And go, say to the Watchers of heaven, who have sent thee to intercede for them: “You should intercede” for men, and not men for you: Wherefore have ye left the high, holy, and eternal heaven, and lain with women, and defiled yourselves with the daughters of men and taken to yourselves wives, and done like the children of earth, and begotten giants (as your) sons? And though ye were holy, spiritual, living the eternal life, you have defiled yourselves with the blood of women, and have begotten (children) with the blood of flesh, and, as the children of men, have lusted after flesh and blood as those also do who die and perish.
Therefore have I given them wives also that they might impregnate them, and beget children by them, that thus nothing might be wanting to them on earth. But you were formerly spiritual, living the eternal life, and immortal for all generations of the world. And therefore I have not appointed wives for you; for as for the spiritual ones of the heaven, in heaven is their dwelling. And now, the giants, who are produced from the spirits and flesh, shall be called evil spirits upon the earth, and on the earth shall be their dwelling. Evil spirits have proceeded from their bodies; because they are born from men, and from the holy Watchers is their beginning and primal origin; they shall be evil spirits on earth, and evil spirits shall they be called.
As for the spirits of heaven, in heaven shall be their dwelling, but as for the spirits of the earth which were born upon the earth, on the earth shall be their dwelling. And the spirits of the giants afflict, oppress, destroy, attack, do battle, and work destruction on the earth, and cause trouble: they take no food, but nevertheless hunger⌉ and thirst, and cause offences. And these spirits shall rise up against the children of men and against the women, because they have proceeded from them. (Book of Enoch, chap. XV)
Here the Lord himself – described in the previous chapter – orders Enoch to remind the watchers all the evil they have done, leaving the sky to join the women on earth. But here there is a crucial change, already mentioned in previous comments.
The author of the previous chapters – roughly until the eleventh – could not explain how the evil continued to be present on earth even after the flood. In the chapter fifteen the human nature of the giants is clearly distinguished from their spirit that continue to live in the earth even after the giants were destroyed by the flood. The giants’s spirits are called evil spirits. These spirits wander on the earth, tempting man to commit evil. At the times of Jesus these spirits are also called impure spirits. These spirits could even seize man making them do bizarre things and separating them from the rest of men. The spirits that came out from the poor man of Gerasa (see Mark 5) took possession of the herd of pigs who then ran violently down a steep place into the sea and were choked in the sea. In so doing the pigs died while the spirits were free to wander on the earth searching for other bodies in which to enter.
So for the second author of the book of the watchers, the origin of evil is clear. It originates from the suggestions that come from evil spirits and that push man to sin. However can choose whether to follow the suggestions of impure spirits or not. Therefore the vision of the second author of the book of Enoch is not totally deterministic.