In the middle of Mormon’s narration of events, he inserts something about his writing, and about who he is. From verse 8 through the end of this chapter (which also ended a chapter in the 1830 edition of the Book of Mormon), we have Mormon describing himself and the reason he is writing his record.
First thing of note is in verse 9. After saying that he cannot write the hundredth part of all of the records, he notes that there is, in addition to the archive of the large plates, “a shorter but true account … given by Nephi.” Mormon is telling us that he is taking some of the account in 3 Nephi from Nephi’s personal record. Even though he announces it at this point, it is not clearly the source until 3 Nephi 8.
Next, we have the introduction of Mormon himself. This is the first time in our current Book of Mormon that we are introduced to the editor who has framed what we have read. Surely in the part of his work that was lost (known as the 116 lost pages), there must have been another introduction to Mormon and why he was writing. Nevertheless, we get it here.
Why here, if it must have been done earlier? The answer is in the next few verses.