(Isa. 29:5)
An ancient nation which lived in America actually was destroyed suddenly, just as Isaiah foretold. Its population numbered in the millions. These people once had been righteous and had prophets among them who kept a sacred history engraved on metal plates. Before their final destruction, one of their prophets buried that record in the ground in a stone container for safe-keeping. Hence, when this book was found, translated, and published in modern times, that early nation literally spoke out of the ground just as Isaiah said it would.
(Mark E. Petersen, Ensign, Nov. 1977, 12.)
These predictions of Isaiah could not refer to Ariel, or Jerusalem, because their speech has not been “out of the ground,” or “low out of the dust,” but it refers to the remnant of Joseph who were destroyed in America… . The Book of Mormon describes their downfall, and truly it was great and terrible. At the crucifixion of Christ, “the multitude of their terrible ones,” as Isaiah predicted “became as chaff that passeth away,” and it took place, as he further predicts, “at an instant suddenly.” Many of their great and magnificent cities were destroyed by fire, others by earthquakes, others by being sunk and buried in the depths of the earth. This sudden destruction came upon them because they had stoned and killed the prophets sent among them. Between three and four hundred years after Christ, they again fell into great wickedness, and the principal nation fell in battle. Forts were raised in all parts of the land, the remains of which may be seen at the present day. Millions of people perished in battle and they suffered just as the Lord foretold by Isaiah.
(Orson Pratt, Orson Pratt’s Works: The Light of Understanding[Salt Lake City: The Deseret News Press, 1945], 270–71.)
In what form or shape or by what method did Moroni restore the everlasting gospel? … God could do only one thing, and that was to raise up a new prophet for this particular purpose, and this He did in the person of the Prophet Joseph Smith, Jr.
In what way did the angel deliver the gospel to Joseph Smith? … The prophet Isaiah explains. In the twenty-ninth chapter of his book, he tells of an ancient record that would come out of the ground in the latter days, in a time preceding the restoration of Palestine as a fruitful field. (See verse 17.) This record would be in the form of a book, he said, having to do with a people who had been destroyed suddenly. (See Isa. 29:5.)
(Mark E. Petersen, Ensign, Nov. 1983, 31.)