The book has five sections, which, though diverse in nature and style, combine to point in a bold direction: In spite of God's best efforts, our world is sometimes out of control.
This very theme propelled the book to huge popularity in Jerusalem 2,000 years ago, when people increasingly felt that something fundamental had gone wrong with the world, that times and practices were changing too quickly, and that an unwelcome modernity was destroying a thousand years of stability and prosperity.
Enoch explained why things seemed to be out of control: they were.
Enoch makes his case early on by contrasting God's perfect plan for the world with the reality that actually ensued.
Enoch goes into some detail about deciduous trees, which grow leaves precisely in the summer when people need shade. These automatic seasonal parasols represent God's perfect universe, which includes a clear plan for small details like trees; a proper path for celestial bodies like the sun, moon and stars; and a defined role for people and angels.
Enoch elaborates on the theme of people and angels. Human men need to marry and reproduce with human women, because humans have finite lifespans. Angels, on the other hand, live forever, so they don't need spouses. But a group of evil holy angels led by Semyaza descended to earth and mated with human women. Enoch's description here meshes perfectly with Genesis 6:1, which describes how "people multiplied ... and daughters were born to them, and the sons of angels took wives for themselves" from among the humans.
These ill-advised unions resulted in giants — nephilim in Hebrew and gigantes in Greek — who devoured everything upon the earth. At the same time, the evil angels also taught humans some of heaven's secrets, like spells, astrology, deception, and metallurgy for warfare. These secrets in turn led humans to such evil behavior as exploitation and adultery.
In short, the once-perfect world had become corrupt, in spite of God's best efforts.
In this sense, the Book of Enoch address the same questions of suffering, fallennes, and good versus evil that we find in the Life of Adam and Eve and the Apocalypse of Abraham. According to the Life of Adam and Eve, suffering is the price we pay for being human. In the Apocalypse of Abraham, suffering is well-deserved punishment for doing or being evil.
But Enoch raises the possibility that human suffering might not be valuable, might not be deserved, and might not even be what God wants. Maybe we suffer only because the world is imperfect.
While this explanation was popular among the population of ancient Jerusalem — and continues to resonate with people in modernity — it was whitewashed from mainstream monotheism by later theologians.