And I have said, “How many in the congregation would like to read the sealed portion of the plates?” And there are many who have not read the Book of Mormon, the unsealed portion.
In verse 21 of 2 Nephi 27, the Lord prophetically forbids Joseph to touch “the things which are sealed” – just as Moroni would later forbid him to do. [2 Ne. 27:21] (See George Q. Cannon, Life Of Joseph Smith the Prophet, Salt Lake City: Deseret Book Co., 1986, p. 45.) Before ending his earthly ministry, Moroni himself wrote to the future translator of his record: “I have told you the things which I have sealed up; therefore touch them not in order that ye may translate; for that thing is forbidden you, except by and by it shall be wisdom in God.” (Ether 5:1)
In the Doctrine and Covenants we have a brief transcript of a writing of John from a leather scroll that Joseph Smith saw in a vision. Since the language of that text is close to the Gospel of John but more expansive and in a more personal tone, we may have in section 7, as well as in section 93, some of John’s earlier or more complete Gospel that we are told will be brought forth in our dispensation (D&C 93:18), depending on our faith. — Book of Mormon Gospel Doctrine Teacher’s Manual
We have not received, by any means, all of the word of the Lord. I think we have received most of the word of the Lord that is required until the Second Coming. The Lord has given all that people in the world have the spiritual capacity to receive at this time. There is going to be another great dispensation, that is, another great period of enlightenment, when he comes; and at that time he will reveal all things, such as the sealed portion of the Book of Mormon. But he will not reveal the sealed portion of the Book of Mormon now, and let us publish it to the world, because what it contains is so far beyond the spiritual capacity of men that it would drive people away from the truth rather than lead them to the truth. Actually, it is an act of mercy for the Lord to limit, to a particular people, the amount of revelation they receive. — Elder Bruce R. McConkie, “This General Shall Have My Word Through You,” BYU Symposium, June 27, 1979
You recollect that when the Book of Mormon was translated from the plates, about two-thirds were sealed up, and Joseph was commanded not to break the seal; that part of the record was hid up. The plates which were sealed contained an account of those great things show unto the brother of Jared; and we are told that all those things are preserved to come forth in the due time of the Lord. — Orson Pratt, Journal of Discourses, vol. 3, p. 347