Nephi understands that Isaiah’s reference to the words of a book that is sealed (Isa 29:11) refers to the golden plates. The sealed portion of these plates has engendered some speculation. What is contained in the sealed portion? When will we get to read that sealed portion? The Book of Mormon answers both of those questions. First of all, Nephi explains that the sealed book contains a revelation covering the events of the entire world’s history, from the beginning of the world to the ending thereof. This is exactly how Mormoni explains it in Ether 3:27:
’And when the Lord had said these words, he showed unto the brother of Jared all the inhabitants of the earth which had been, and also all that would be; and he withheld them not from his sight, even unto the ends of the earth.
For he had said unto him in times before, that if he would believe in him that he could show unto him all things--it should be shown unto him; therefore the Lord could not withhold anything from him, for he knew that the Lord could show him all things.
And the Lord said unto him: Write these things and seal them up; and I will show them in mine own due time unto the children of men.’ (Ether 3:25-7)
The brother of Jared had such faith that he was given this revelation—a history of the inhabitants of the earth from beginning to end. It would contain all things…which ever have been among the children of men, and which ever will be even unto the end of the earth (v. 11). Had this revelation been translated by Joseph Smith, we would likely have a much clearer picture of the events that are to transpire at the time of the Second Coming. Instead, they are given to us in the figurative language of John the Revelator. The brother of Jared’s words would have been written to our understanding and would contain the great power that Moroni prayed about, the things which he (the brother of Jared) wrote were mighty even as thou art, unto the overpowering of man to read them (Ether 12:24).
Nevertheless, the Book of Mormon was written to go forth to a wicked world, and the things which are sealed shall not be delivered in the day of the wickedness and abominations of the people (v. 8). Therefore, some of the most holy and sacred revelations must be withheld until the world is ready. This is why Nephi couldn’t record all of the vision which he saw (1 Nephi 14:25), it is why the other Nephi couldn’t record those things which Christ prayed for them (3 Nephi 17:17), and it is why Paul couldn’t speak of the words which he heard when he was caught up to the third heaven, he was caught up into paradise, and heard unspeakable words, which it is not lawful for a man to utter (2 Cor 12:2-4).
Joseph Smith
“Paul ascended into the third heavens, and he could understand the three principal rounds of Jacob’s ladder-the telestial, the terrestrial, and the celestial glories or kingdoms, where Paul saw and heard things which were not lawful for him to utter. I could explain a hundred fold more than I ever have of the glories of the kingdoms manifested to me in the vision, were I permitted, and were the people prepared to receive them.” (Teachings of the Prophet Joseph Smith, p. 304)
Joseph Fielding Smith
“Now the Lord has placed us on probation as members of the Church. He has given us the Book of Mormon, which is the lesser part, to build up our faith through our obedience to the counsels which it contains, and when we ourselves, members of the Church, are willing to keep the commandments as they have been given to us and show our faith as the Nephites did for a short period of time, then the Lord is ready to bring forth the other record and give it to us, but we are not ready to receive it. Why? Because we have not lived up to the requirements in this probationary state in the reading of the record which had been given to us and in following its counsels.” (Conference Report, Oct. 1961, pp. 19-20 as taken from Latter-day Commentary on the Book of Mormon compiled by K. Douglas Bassett, p. 156)