The Book of Jacob is the third book of the Book of Mormon. Its full title is The Book of Jacob: The Brother of Nephi. According to the text, it was written by the ancient prophet Jacob, brother of the prophet Nephi, believed to have lived during the 6th century BC.
While this book contains some history of the Nephites, including the death of Nephi, it is mainly a record of Jacob's preachings to his people. Chapter 5 contains The Parable of the Olive Tree, a lengthy allegory of the scattering and gathering of Israel, comparing the Israelites and gentiles to tame and wild olive trees, respectively.