Nephi recontextualizes and expands virtually every line in the first part of the Isaiah verse so that it prophesies the coming forth of his people’s words. Subtly, he redefines the concept of a “sealed” book.
Joseph Blenkinsopp, an Isaiah scholar who would not consider this passage fulfilled by the Book of Mormon, proposes this reading:
We hear of the committing to writing and sealing (i.e., notarizing and thus authenticating) of prophecies on two occasions in the book. After the failure of Isaiah’s intervention in international politics under Ahaz, the prophetic testimony and teaching—referring to prophecies delivered during that crisis—were sealed and committed to disciples for safekeeping. This is at least a defensible interpretation of 8:16–18. Much the same happened during the critical period leading up to Sennacherib’s punitive expedition some three decades later. The prophet is told to write his words on a tablet and a scroll as a witness to those who were attempting to prohibit him from fulfilling his appointed role (30:8–11). A similar situation confronted Jeremiah, prohibited from addressing the public in the temple precincts, with the result that he committed his words to writing instead (Jer. 36:4–6). In the context of this section of Isaiah (28–31) the prophecy would presumably have dealt with the consequences of relying on an Egyptian alliance. In speaking of the book’s reception, the glossator of 29:11–12 took in a broader field of vision. He seems to refer to two types of readers: those who will not take the trouble, or who disingenuously do not consider themselves qualified to break the seal, that is, to decrypt the prophetic writings; and those whose ignorance and spiritual insensitivity rule out even the attempt to grasp what is written.
The practice of “sealing” a document was a means of authenticating or legitimizing it. Jezebel “seals” letters to indicate that they come from the authority of the king: “So she wrote letters in Ahab’s name, and sealed them with his seal, and sent the letters unto the elders and to the nobles that were in his city, dwelling with Jabot” (1 Kgs. 21:8). Similarly, when the people of Israel renew their covenant with Yahweh, they signify their acceptance by sealing it: “And because of all this we make a sure covenant, and write it; and our princes, Levites, and priests, seal unto it” (Neh. 9:38). Legal documents might be sealed, but they could also have a summary of the contents written on the outside, hence the reference in Revelation 5:1 to “a book written within and on the backside, sealed with seven seals.”
However, the physical appending of an official seal was not the only meaning for a “sealed” book. In the book of Daniel, Daniel sees a divine personage and hears something about the end of times but does not understand clearly:
And I heard the man clothed in linen, which was upon the waters of the river, when he held up his right hand and his left hand unto heaven, and swore by him that liveth for ever that it shall be for a time, times, and an half; and when he shall have accomplished to scatter the power of the holy people, all these things shall be finished.
And I heard, but I understood not: then said I, O my Lord, what shall be the end of these things?
And he said, Go thy way, Daniel: for the words are closed up and sealed till the time of the end. (Dan. 12:7–9)
Although the sealing of these words may also imply authority, the seal closes off those words from public knowledge. The seal effectively hides the words that are not to be known until the “time of the end” when the seal will be broken. Nephi customized the concept of sealing to the characteristics of the Book of Mormon. The Book of Mormon will be “sealed,” first, because the meaning will be hidden until it is translated; second, because it has been hidden from the world; and third, because it is authenticated (sealed by the testimony) of its prophet writers.
In addition to these meanings for Nephi’s discussion of Isaiah, there are two overall sealings that apply to the content of the Book of Mormon. The first is mentioned on the title page (“Written and sealed up, and hid up unto the Lord… ”). The entire work is “sealed.” That sealing means it is not available for reading, either because it was hidden, or because it was in a language that could not be understood. The second is a sealing on a section in Ether which is “a revelation from God, from the beginning of the world to the ending thereof” (Ether 3:25–27).