Was Jacob 5 written by a person other than Jacob or Joseph Smith? I do not think Jacob could possibly have written this. He did not have the botanical knowledge or agricultural experience, so while it is in the Book of Jacob, it was not written by Jacob. Jacob says that Zenos wrote these words to all the house of Israel. And indeed, there is evidence of different authorship here, including difference with any other author in the Book of Mormon either. Mormon did not write this. Nephi did not; he had gone, and his vocabulary was different.
In the 600-page book, The Allegory of the Olive Tree: The Olive, the Bible, and Jacob 5, hundreds of details in this amazing text are probed in depth. For example, in chapter nine, called "Words and Phrases in Jacob 5," I went through and tabulated how many vocabulary words we have in this lengthy chapter. There is a very small vocabulary to this allegory, but it is also a very distinctive vocabulary. There are 30 phrases or expressions in Jacob 5 that never appear again anywhere in the Standard Works. There are also seven idioms that are found in the early chapters of Genesis but nowhere else in the Bible or Book of Mormon. They are part of the Creation account, pertaining to how God created the world and the House of Israel. There are 21 further expressions that are found in Jacob 5 and in other Old Testament texts, but which don’t show up in the New Testament, and so on. As a whole, Zenos’s vocabulary does not belong to any other writer known to us in the scriptures.
This writing style is just one more important indication that this exquisite prophetic text was not written by anyone other than Zenos. It is an inspired work of a person who lived long ago, probably lived in Palestine somewhere, and was filled with a deep understanding of the mission and the plan of God for the House of Israel. Zenos embedded that synoptic vision in an elegant allegory that endures and continues to inspire us today in many ways. What a gem this great allegory is!
Could Joseph Smith have written this? As one of the authors in The Allegory of the Olive Tree, botanist Wilford M. Hess, concluded: "Joseph Smith probably had little knowledge of olive trees in New York, as they will not grow in the northeastern United States." While some information on that topic was available in the Bible and other books from Joseph Smith’s time, the details were sparse.
Wilford M. Hess, Daniel J. Fairbanks, John W. Welch, and Jonathan K. Drigss, "Botanical Aspects of Olive Culture Relevant to Jacob 5," in The Allegory of the Olive Tree: The Olive, the Bible, and Jacob 5, ed. Stephen D. Ricks and John W. Welch (Provo and Salt Lake City, UT: FARMS and Deseret Book, 1994), 507.
John W. Welch, "Words and Phrases in Jacob 5," in The Allegory of the Olive Tree: The Olive, the Bible, and Jacob 5, ed. Stephen D. Ricks and John W. Welch (Provo and Salt Lake City, UT: FARMS and Deseret Book, 1994), 174–184.