The Book of Jasher is mentioned in Joshua, Samuel, and Timothy. Why was it not included in the Bible, or do we even know? Why would it have been omitted by the Council of Nicea? The Book of Jasher seems to give a much more detailed account of creation, but also many other biblical stories. Why the taboo?
The short answer is that we don’t have the Book of Jasher in our Bibles because the book has never been discovered. There are two books called the Book of Jasher in existence today, one is a forgery from the 18th century that claims to be the lost book and the other a Hebrew midrash from the 16th century.
Here are several articles that talk about the various occurrences in more depth.
This first one is from the Jewish Virtual Library and talks about the contents of the lost book that can be extracted from the biblical mentions of it: https://www.jewishvirtuallibrary.org/book-of-jashar.
The second is the Wikipedia article about the lost book that talks more about the various titles given to the book: https://en.wikipedia.org/wiki/Book_of_Jasher_(biblical_references).
The third is the Wikipedia article about the Hebrew midrash: https://en.wikipedia.org/wiki/Sefer_haYashar_(midrash).
The fourth is the Wikipedia article about the forgery that you can buy now on Amazon: https://en.wikipedia.org/wiki/Book_of_Jasher_(Pseudo-Jasher).
You can be forgiven for being confused!
-- Rev. Anne Robertson - Executive Director - Massachusetts Bible Society