The context for this verse is perhaps enigmatic. It is possible that the verse sets up the conflict with Korihor that will begin in verse 6. Seen in this context, Mormon is foreshadowing the conflict between Korihor and Alma as a conflict between the law of Moses and the doctrine preached by Korihor. This is not a very satisfying possibility, however, as the real conflict that will be presented is between Korihor’s doctrine and the belief in the Atoning Messiah, which is a central aspect of the Nephite religion, but not one that Mormon has closely tied to the law of Moses. Indeed, since it is Mormon who is writing the document, and the law of Moses was done away in Christ, an event Mormon knows to have taken place, where this text only hopes for the arrival of the Savior, we might expect that the conceptual distance between the law of Moses and the gospel of Christ might be rather far in Mormon’s mind.
The second possibility is that this verse looks back to the mourning rites for the dead. Certainly there would have been ritual associated with the burial of so many, and the statement that they obeyed the law of Moses might be seen as applying to the burial of the slain rather. Thus there may have been a greater tie between the Old World funeral customs listed above and the those of the Nephites, even though we have so little of them in the text.