Had Joseph Smith been the author of the Book of Mormon, chapter 9 of 2 Nephi would have been quite a doctrinal feat. Monte Nyman quotes Joseph Fielding Smith as saying that 2 Nephi 9 is "one of the most enlightening discourses ever delivered in regard to the atonement" (Answers 4:57). Nyman also describes a number of additional doctrines that are brought to light:
(1) The first doctrine is that the institution of the church existed in Old Testament times. This doctrine is not readily accepted in the world. Jacob prophesied that the Jews would "be restored to the true church" (2 Nephi 9:2). Logically, one cannot be restored to a church which has not already been established. It is interesting that Stephen, in his great martyrdom speech, referred to "the church in the wilderness" at the time of Moses (see Acts 7:38). Nephi also referred to "the brethren of he church" (see 1 Nephi 4:24-26).
(2) The second doctrine concerns education. Jacob warned not to trust only the mind of man, but he noted, "to be learned is good if they hearken unto the counsels of God" (2 Nephi 9:28-29).
(3) A third doctrine is that the only way into heaven is through Jesus Christ. Contrary to the teaching of modern Christianity that Peter guarded the pearly gates, Jacob declares: "The keeper of the gate [to eternal life] is the Holy One of Israel; and he employeth no servant there" (2 Nephi 9:41).
[Monte S. Nyman, "Come to Understanding and Learn Doctrine," in The Book of Mormon: Second Nephi, The Doctrinal Structure, pp. 24-25]