Mosiah 8:13

13 Now Ammon said unto him: I can assuredly tell thee, O king, of a man that can translate the records; for he has wherewith that he can look, and translate all records that are of ancient date; and it is a gift from God. And the things are called interpreters, and no man can look in them except he be commanded, lest he should look for that he ought not and he should perish. And whosoever is commanded to look in them, the same is called seer.

President Joseph Fielding Smith said:

“King Mosiah possessed ‘. . . two stones which were fastened into the two rims of a bow’ [Mosiah 28:13] called by the Nephites ‘Interpreters,’ with which he translated the Jaredite record [Mosiah 28:11–14], and these were handed down from generation to generation for the purpose of interpreting languages. How Mosiah came into possession of these ‘two stones’ or Urim and Thummim, the record does not tell us, more than to say that it was a ‘gift from God’ [Mosiah 21:28]. Mosiah had this ‘gift’ or Urim and Thummim before the people of Limhi discovered the record of Ether. They may have been received when the ‘large stone’ was brought to Mosiah with engravings upon it, which he interpreted by the ‘gift and power of God’ [Omni 1:20–21]. They may have been given to him, or to some other prophet before his day, just as the brother of Jared received them—from the Lord.

“That the Urim and Thummim, or two stones, given to the brother of Jared were those in the possession of Mosiah appears evident from the following statements in the Book of Mormon:

“The brother of Jared was commanded to seal up his writings of the vision he had when Christ appeared to him, so that they could not be read by his people. This vision was in a language which was confounded, for it was not to go forth until after the resurrection of Christ. The Urim and Thummim were also sealed up so that they could not be used for the purpose of interpreting those sacred writings of this vision, until such time as the Lord should grant to man to interpret them. When they were to be revealed, they were to be interpreted by the aid of the same Urim and Thummim [Ether 3:21–28]. . . .

“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 [D&C 17:1].”

(Answers to Gospel Questions, comp. Joseph Fielding Smith Jr., 5 vols. [1957–66], 1:160–62.)