Jacob, a younger son of Lehi and Sariah born during the family's wilderness journey, narrates this book in a voice distinct from his brother Nephi's: less narrative, more sermon. Jacob addresses his people directly on themes of wealth, pride and fidelity, and includes some of the small plates' sharpest social criticism, condemning the accumulation of riches and the mistreatment of women within the community he is addressing.
The book's best known section is an extended allegory, which Jacob presents as a quotation from an otherwise unknown prophet named Zenos, describing the owner of a vineyard who grafts branches from a wild olive tree into a tame one and tame branches into wild trees in an effort to preserve the vineyard's fruit. The allegory runs for an entire chapter and is generally read within the tradition as a figure for the scattering and eventual gathering of the house of Israel. Because Zenos is not otherwise attested outside the Book of Mormon, the allegory has drawn particular attention from scholars studying the text's use of unknown or unattested sources.
The vineyard allegory is unusually long for the small plates, running to a full chapter of sustained metaphor rather than the shorter prophetic bursts more typical of the surrounding text, and later Latter-day Saint commentary has treated it as a structural key to how the whole Book of Mormon frames Israel's scattering and gathering.