All of these verses were once a part of the original text of Isaiah but were lost (see JST, Isaiah 29:11–19). They contain many great truths, and should be studied as part of the text of Isaiah 29. The opening phase in verse 11 of the KJV—”And the vision of all”—is an authentication of the contents of the sealed portion of the record, “a revelation from God, from the beginning of the world to the ending thereof” (v. 7). Moroni gives us more information about its contents further verifying “the vision of all.” He said it contained the vision shown unto the brother of Jared of “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” (Ether 3:25).
The things that were sealed were not to be delivered in the day of the wickedness of the people (v. 8). The things sealed were to come forth in “the due time of the Lord” (v. 10). The Lord commanded the brother of Jared to “Write these things and seal them up; and I will show them in mine own due time unto the children of men” (Ether 3:27). The Lord further qualified the due time of the Lord to Moroni:
6 For the Lord said unto me: They shall not go forth unto the Gentiles until the day that they shall repent of their iniquity, and become clean before the Lord.
7 And in that day that they shall exercise faith in me, saith the Lord, even as the brother of Jared did, that they may become sanctified in me, then will I manifest unto them the things which the brother of Jared saw, even to the unfolding unto them all my revelations, saith Jesus Christ, the Son of God, the Father of the heavens and of the earth, and all things that in them are. [Ether 4:6–7]
In abridging the Jaredite record, Moroni addressed the future translator about “the things which have been sealed up; therefore touch them not in order that you may translate” (Ether 5:1). Joseph did not translate the sealed part, but “the day cometh that the words of the book that were sealed shall be read upon the housetops; and they shall be read by the power of Christ; and all things shall be revealed” (v. 11). How these things shall be read from the housetops is not specified, but with today’s miracles of radio, television, satellite, and the internet, it is easy to see how it might happen (compare D&C 88:5–13).
Isaiah also foresaw the three witnesses to the Book of Mormon; Oliver Cowdery, David Whitmer, and Martin Harris (v.12). Their testimony is in the front of every copy of the Book of Mormon. The few others who were to bear testimony of his word (v. 13) include the eight witnesses whose testimony is also in the front of the Book of Mormon.