The people of Limhi brought to Mosiah a record, ‘… engraven on plates of ore, ’ which record Mosiah translated by the aid of ‘two stones which were fastened into the two rims of a bow, ’ and which gave an account of the Jaredites. In translating this record Mosiah kept from going forth to the people that particular part forbidden of the Lord to be revealed until after he was lifted up upon the cross. These sacred revelations given to the brother of Jared were kept from the Nephite people, as well as many other things, until after the resurrection of Christ [see Alma 63:12]. After the appearing of the Savior to the Nephites, the vision of the brother of Jared was revealed to the Nephites.
When Moroni made his abridgment of the record of Ether, he copied on his record the vision of the brother of Jared. At the command of the Lord, however, Moroni also sealed up the greater things in this vision and the ‘interpreters’—which were the same ‘two stones’ had by the brother of Jared, so that this vision should not be made known even in our day among the Gentiles, in the day of their wickedness [see 2 Nephi 27:8]; ‘… until the day that they shall repent of their iniquity, and become clean before the Lord.’ So we today do not have the fulness of the account written and sealed up by the brother of Jared and again sealed by Moroni. This part of the record the Prophet Joseph Smith was forbidden to translate. We have, then, received but the ‘lesser part.’
Joseph Smith received with the ‘breastplate’ and the plates of the Book of Mormon, the Urim and Thummim, which were hid up by Moroni to come forth in the last days as a means by which the ancient record might be translated, which Urim and Thummim were given to the brother of Jared.
(Joseph Fielding Smith, Answers to Gospel Questions, 1:161–62)