B. H. Roberts writes of the coming forth of the Book of Mormon for the Church's official centennial history.
B. H. Roberts, A Comprehensive History of the Church of Jesus Christ of Latter-day Saints, 6 vols. (Salt Lake City: The Church of Jesus Christ of Latter-day Saints, Deseret News Press, 1930), 1:71–73, 125, 129–130
At this point in his message the angel told the Prophet that a book was deposited in a hill not far distant, written upon gold plates, giving an abridged history of the former inhabitants of the American continents, and an account of their origin. He also said that the fulness of the gospel of Jesus Christ was contained in this book as delivered by the Savior to the ancient inhabitants of America; that with this record were two stones held in silver bows and fastened to a breast-plate, constituting "Urim and Thummim," or "Interpreters." The possession and use of these stones constituted men "Seers" in ancient times, and God had prepared these for the purpose of translating the before mentioned book. After communicating this information Moroni commenced quoting prophecies from the Old Testament, beginning with the third chapter of Malachi, most likely the first part of the chapter, as that deals with the coming of the messenger to prepare the way for the glorious coming of the Messiah, a theme a propos to the developing mission of the Prophet.
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He was commanded that when the ancient American record, or Book of Mormon, would be given to him for translation, be must not show the plates, or the interpreters, or the breast-plate to any persons except those to whom he would be commanded to show them. This under penalty of his own "destruction." While conversing upon these matters, the young Prophet's vision was quickened and be beheld the bill in which the Nephite record was deposited, and so distinct was the vision that he easily recognized the place the next day on visiting it.
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With the coming forth of the Book of Mormon there are associated superhuman events. What men usually call miraculous events. The book's existence was revealed by Moroni, an ancient American Prophet, now raised from the dead, and co-operating with Joseph Smith to bring forth to the world this record of an ancient people. The integrity of this whole story unfolding in the text of these pages depends upon the reality of these things.
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The sum of the whole matter, then, concerning the manner of translating the sacred record of the Nephites, according to the testimony of the only witnesses competent to testify in the matter is: With the Nephite record was deposited a curious instrument, consisting of two transparent stones, set in the rim of a bow, somewhat resembling spectacles, but larger, called by the ancient Hebrews Urim and Thummim, but by the Nephites Interpreters. In addition to these Interpreters the Prophet Joseph had a Seer Stone, which to him was as Urim and Thummim; that the Prophet sometimes used one and sometimes the other of these sacred instruments in the work of translation; that whether the Interpreters or the Seer Stone was used the Nephite characters with the English interpretation appeared in the sacred instrument; that the Prophet would pronounce the English translation to his scribe, which, when correctly written, would disappear and other characters with their interpretation take their place, and so on until the work was completed.