Verse 15 tells us that books were chiefly kept by Nephites, and then verse 16 gets interesting. These books “have been handed down from one generation to another by the Nephites, even until they have fallen into transgression….” Obviously the books did not fall into transgression. The sense of the verse must be that the Nephites fell into transgression. The “until” is the interesting part. There is some connection between the books and the transgression of the Nephites, but what? What Mormon tells us of the transgressing Nephites is that they “have been murdered, plundered, and hunted, and driven forth, and slain, and scattered upon the face of the earth, and mixed with the Lamanites…..” All of these things certainly describe the people, but why the tie to the books? I would suggest that Mormon is saying that the books went with them.
Mormon is a man of the ancient world, and in the ancient world it is most typical for people to assume that their own people are the center of the universe, and the source of everything that is important. What Mormon appears to be saying here is that there are many books available in his day, and many of them are in and about the people of the land northward. Since books are good, Mormon needs to explain how these Lamanites got them, and he suggests that it was apostate Nephites who “took” books, or the knowledge of writing, to these other peoples. In these verses, Mormon is explaining that other cultures have many of the benefits of the Nephite culture because of apostate Nephites. In this particular case, it is books.