The Book of Mormon, as we now have it, consists of the following:
“Plates of Nephi”
Mormon’s abridgment of the large plates of Nephi and some of his other writings (Mosiah through Mormon 7, Moroni 7-9)
“After I Had Made an Abridgment from the Plates of Nephi”
Mormon was given two assignments: (1) he was to continue to record the doings of his own day and time on what we know as the large plates of Nephi; and (2) he was to abridge the large plates themselves, writing this abridged record on what we now call the plates of Mormon.
Of his work of abridgment, Mormon wrote:
“There had many things transpired which, in the eyes of some, would be great and marvelous; nevertheless, they cannot all be written in this book; yea, this book cannot contain even an hundredth part of what was done among so many people… . But behold there are records which do contain all the proceedings of this people; and a shorter but true account was given by Nephi.
Therefore I have made my record of these things according to the record of Nephi, which was engraven on the plates which were called the plates of Nephi. And behold, I do make the record on plates which I have made with mine own hands.”
In his own words, Mormon further explained that he made the record
“from the accounts which have been given by those who were before me, until the commencement of my day; and then I do make a record of the things which I have seen with mine own eyes.” (3 Nephi 5:8-11, 16-17.) Mormon observed that he, knowing that all things would be made known in a future day, “and also that a knowledge of these things must come unto a remnant of these people, and also unto the Gentiles, … I write a small abridgment, daring not to give a full account of the things which I have seen”
(Mormon 5:9).