At the beginning of his book, Jacob states the essence of the commandment that Nephi gave to him pertaining to writing on the Small Plates. He was told to touch only lightly on the history, to record sacred preaching, to summarize great prophecies, and do this all for Christ’s sake. Interestingly, Jacob does exactly that. We don’t get much history in the book of Jacob. His preaching in Jacob 2–3 deals with sacred matters, including chastity and consecration. His summations in Jacob 4 and 6 of the prophecy of Zenos in chapter 5 help focus the allegory of the olive tree on Christ. And the episode with Sherem in Jacob 7 affirms, for the peace and benefit of the people, the legitimacy of prophesying about the coming Christ (doing this is not false prophecy), of teaching the people to worship Christ (doing this is not leading people into apostasy), and of calling Christ a divine being (doing that is not blasphemy), as Sherem had accused.
Furthermore, in verses 5–8, Jacob certifies that he and his people had received many revelations, and that they labored to bring people to Christ and not to offend God, which would disqualify them from remaining in their new land of promise. He specifically stated that he took it upon himself to fulfill the commandment of his brother Nephi. Some people wonder why the books on the Small Plates are so short. One reason is that these authors all follow Nephi’s specific instructions very meticulously as their guiding instruction.
Book of Mormon Central, "Why Do the Authors on the Small Plates Follow a Pattern? (Jacob 7:27)," KnoWhy 74 (April 8, 2016).
John W. Welch, "The Father’s Command to Keep Records in the Small Plates of Nephi," FARMS Preliminary Report (September 1984), 1–12.