Within the Book of Mormon, as a new volume of scripture, is the caution that even it is incomplete. What a marvel that is if you think about it. Here's a new revelation telling us that there are other revelations that aren't included in either the Book of Mormon or the Bible.
Everyone nation, from time to time, received sacred messages from the Lord! No matter where they are - east, west, north or south, He's been in touch. They have written it down. The records are sacred, and He watches over them. They will be revealed. And, the good/bad news is that from their content we will be judged.
We are judged "according to our works," but measured against "that which is written." Think about that for a moment.
What if they haven't come to light yet? Are they still written? Are they still going to be used to measure us? If we haven't seen these words, why would it be appropriate for them to be used as a measuring stick for our conduct? Was the Book of Mormon's standards binding upon us even before the record came forth?
Why does He assure us He is unchangeable? Why does He assure us He is the same yesterday, today and forever? Is the standard going to change from ancient record to ancient record? If it does not change, then are we accountable for the same standard of conduct no matter when or where we live? How can we be held to account for things that are yet to be revealed?
If we cannot be judged against something we do not know (Mosiah 3: 11), how can these words set a standard for judging even before they are published?
I want to propose a concept that appeals to my mind. When we are trying to "prove" a proposition, it is possible to set up an experiment where we control all variables but one, then see what that one variable does. How it acts, or reacts. Life here is like that, I think. A fallen Telestial Kingdom, "or the world in which you presently reside"-- to quote an authoritative source-- is the same place for Able and Cain, Enoch and Noah, Abraham and Nimrod, Moses and Pharoah, Jesus and Ciaphus, Jacob and Sherem, Alma and Nehor, Joseph Smith and Thomas Sharp. Same place with all of these contemporaries. But with the exception of Enoch and Noah, (who took different routes, but nonetheless were both favored by God) all the other pairs had dramatically different outcomes? Why?
This world is a fallen, but controlled environment. We get introduced here with free will and the capacity to change. Inside that environment of a fallen world, there have been people who have come and lived with all the same limitations that we have, but who have grown to know God. Their lives are proof that it can happen. Their testimonies and records of success are part of the "proof" of God's fairness and of mankind's freedom to return to Him.
If the Bible and the Book of Mormon both attest to the fact that it is possible for mankind to overcome by faith and return to God's presence, then we have the proof needed to see how this life should be lived. We have the evidence of God's willingness to receive us, and of our own capacity to overcome and return to Him.
Testimony after testimony, experience after experience are recounted in the Book of Mormon. We have enough "proof" that this process is available and works. If we were to have more, in a different record, reaffirming the same thing involving other people, would it add any different proof than is already in our possession? If not, then can we be judged by the same standard without having the specific life stories before us to illustrate in another hundred ways how men have triumphed and men have failed?
Is it possible there are others, some of whom are still living, who may also have recorded unspeakable things? Do their words count? Are they binding upon us for no other reason than to prove that in this contemporary world of sin it remains still possible to return to God's presence?
What interesting things the Book of Mormon raises for our pondering and edification. It is a revolutionary book, in the sense it revolutionizes our understanding of how God deals with mankind.