And now I, Mormon, being about to deliver up the record which I have been making into the hands of my son Moroni, behold I have witnessed almost all the destruction of my people, the Nephites.And it is many hundred years after the coming of Christ that I deliver these records into the hands of my son; and it supposeth me that he will witness the entire destruction of my people. But may God grant that he may survive them, that he may write somewhat concerning them, and somewhat concerning Christ, that perhaps some day it may profit them (W of M vv. 1-2).
So Mormon supposes (or, rather, "it supposeth him," a construction which is to the best of my knowledge unique to the Book of Mormon) that his son Moroni will live to see the entire destruction of the Nephites. He prays that Moroni will "survive" the Nephites -- meaning that he will continue to live after all the other Nephites have been killed, for that is the meaning of survive when it is used transitively, as detailed in Webster's 1828 dictionary, the standard reference for English as used by Joseph Smith and his contemporaries.
Webster expresses most people's natural sentiments when he gives as an example the sentence, "Who would wish to survive the ruin of his country?" But Mormon positively prays that his son will survive not only the ruin of his country but the "entire destruction" of his people. Why? To quote the key sentence again:
But may God grant that he may survive them, that he may write somewhat concerning them, and somewhat concerning Christ, that perhaps some day it may profit them.
Each of the three instances of them must have the same antecedent: "my people, the Nephites." No other reading is possible. Mormon wants Moroni to outlive all the other Nephites so that he can write about the Nephites -- which I suppose makes sense, since the full story of the Nephites cannot be written until after that story has ended. And why is it important to write about the Nephites? "That perhaps some day" -- in the future, long after the Nephites are extinct -- "it may profit them," meaning the Nephites.
The only sense I can make of this is that Moroni's writings will profit beings who once lived as Nephites but have since moved on to another state. I would assume that spirits and resurrected beings would remember their own history and would have no need (and in the case of spirits perhaps no ability) to read a book about it. It makes the most sense if we assume that the writings will help reincarnated Nephites, who having passed through the veil of forgetfulness would have no knowledge of their own past lives as Nephites, or even of the fact that there ever were any such people as the Nephites.
