A summary of my work on Words of Mormon: Why it was the Lord who made Words of Mormon into a transitional book, and not Mormon.
Mormon begins Words of Mormon with an explanation that he has written the abridgment on separate plates and is about to hand them over to Moroni. He also explains that he has decided to put the small plates with his abridgment. Whether or not he adds them, physically, to his record is not clear. (Perhaps Moroni did the physical adding? He was the one responsible for the addition of the sealed portion.) What does seem clear is that he considers the small plates to be a separate record, even when they are added to the abridgment.
Mormon finds the small plates after he reads about King Benjamin receiving them from Amaleki. He is pleased with the prophecies and hopes the remnant of Lehi’s people will receive them someday. It seems to be this very thing – being pleased with the prophecies – that induces his own writing on the small plates. It seems possible to me that he added a record to the small plates that was longer than we have, though still relatively short, called the Words of Mormon, which likely mainly contained prophecies of Christ (from Benjamin, Abinadi, Samuel the Lamanite, etc.) and their fulfillments.
Our scriptures of course contain a very small Words of Mormon. However, this does not seem to me to be the way Mormon wrote it. There is a feeling in the several times in Words of Mormon where he introduces what he is about to do that he intends to write much more; or, in other words, if he intended to write so little, why spend so much time getting going?
I could assume that I was being overly picky about this, except that D&C 10:41 seems to make clear that the small plates were longer than what we currently have. D&C 10 is where Joseph is told to translate the small plates and use that to replace the lost 116 pages. In verse 41, Joseph is told to translate until he comes to Benjamin. That seems odd, since Benjamin himself never wrote on the small plates; we have to assume it refers to either Amaleki’s writing or Words of Mormon, both of which end by talking about Benjamin. But if he has to be told when to stop, then doesn’t that mean there was more that potentially could have been translated?
In this case, Words of Mormon likely went on for several chapters, and Joseph was told to stop with Benjamin since the small plates were now becoming a replacement for the Book of Lehi and needed to fit in with the abridgment. Had the 116 pages not been lost, likely we would have all of the Words of Mormon, and in their original location in the gold plates – near the end of the Book of Mormon (before the Book of Ether? After?).
It seems then that it is the Lord who is choosing to make the Words of Mormon into a “transition.” He tells Joseph where to stop translating the small plates, he tells him to use this “record of Nephi”instead of the 116 pages, and he tells him that when he translates up through Benjamin, it will match up with “that which ye have retained.” In other words, there was already something to connect up to. The Lord directed the translation (telling Joseph how much of Words of Mormon to translate) so now the two would work together into a single record.
This explains why Words of Mormon serves as transition, even though it did not seem to have that particular purpose originally. It also explains why it ends so abruptly and after repeated introductions/prefaces to Mormon’s words about Benjamin.