Imagine Genesis, except an angel reads it to Moses and adds what got left out. That is the Book of Jubilees.
Who did Cain marry? Her name was Awan, his sister. How did he die? His house fell on him, with stones, because he killed Abel with a stone. Why did Abraham leave home? Because he burned down his father’s house of idols. Every event gets a date, counted in units of 49 years.
The calendar is the point
The book’s real concern is time. It insists on a 364-day solar year, exactly 52 weeks. In that system a festival falls on the same weekday every year, so a holy day never collides with the Sabbath.
It also means that if you keep a lunar calendar, you are celebrating the feasts of God on the wrong days. For the author this is a serious charge. And for a community keeping one calendar, the neighbors keeping another were not simply being different. They were out of step with heaven.
The community at Qumran seems to have agreed. They left around fifteen copies of Jubilees, more than most biblical books, and one of their rulebooks cites it by name. Their calendar may be one reason they withdrew to the desert at all.
What else is in it
The book adds a chief of evil spirits called Mastema, who tests Abraham and attacks Moses. It says that when the Watchers were bound, Mastema asked God to leave a tenth of their spirits free, and God agreed. It says angels taught Noah medicine so that people could survive what remained.
This is where you can watch biblical interpretation happening in real time. Later Judaism and Christianity took much of their thinking about angels and demons from books like this one, and then set the books aside.
Why it fell away
It lost on the calendar. The practice that became rabbinic Judaism did not keep it, and Christians in the Greek and Latin worlds had little use for a book concerned with Jewish festival dates. Greek and Latin copies disappeared.
Ethiopia kept it, as it kept Enoch. Scholars knew the full text only from Ge’ez until the Hebrew fragments surfaced at Qumran and proved the original language.
Where to start
Read chapters 1-5 next to Genesis 1-4, and notice what the author feels the need to fix. That is the fastest way to understand what kind of book it is.
Common questions
What is the Book of Jubilees?
A second-century BC retelling of Genesis and part of Exodus, presented as an angel's dictation to Moses on Sinai. It is sometimes called the Little Genesis, and it divides all of history into 49-year jubilee periods.
Why is the Book of Jubilees not in the Bible?
Its calendar and legal rulings conflicted with the practice that became mainstream Judaism, so it was not accepted there, and Christians in the Greek and Latin worlds had no reason to preserve it. The Ethiopian church did, and it is canon there.
What does Jubilees add to Genesis?
Names, dates and rules. It names Adam's daughters and Cain's wife Awan, reports that Cain was killed when his house fell on him, introduces a chief of evil spirits called Mastema, and dates events to the exact year and week.