This Mosiah, the son of King Benjamin, was the last of the kings of Zarahemla, preceding the Judges. He was the translator of the contents of the twenty-four plates of gold which were delivered to him by the hands of Limhi. The translation was made by the means of those two stones which were fastened into the two rims of a bow. The stones, we read in the Book of Mormon, were prepared from the beginning, and were handed down from generation to generation, for the purpose of interpreting languages. (Mosiah 28:11-14) They were in all probability the stones which were given to Moriancumer, and, later, to the Prophet Joseph by the resurrected Prophet of the Nephites, Moroni.
How did King Mosiah get them?
We turn to the Book of Omni. We read there that during the reign of the first Mosiah, the father of King Benjamin, a large stone with engravings thereon was brought to Zarahemla to the king. The king translated the text thereof by the gift and power of God, and found that it contained an account of one Coriantumr and the slain of his people. Amaleki, the chronicler, adds the explanation that Coriantumr had been found by people from Zarahemla—perhaps by hunters—and that he had lived with them nine moons (we presume months) of his life.
Coriantumr was the last of the kings of the Jaredites of whom we have any historical record, as Ether was the last of their prophets. He fought his savage enemy, Shiz, at Ramah, until both their armies were annihilated. Then he ended the life of his antagonist. He, himself, was left on the battlefield apparently lifeless. But Coriantumr recovered, and began his pilgrimage which eventually ended in Zarahemla. As the head of the government of the Jaredite Kingdom, he may have had charge of the Urim and Thummim and brought them where King Mosiah at last obtained them, together with the historical stone (Omni 19-22).
LIMHI AND AMMON
In the first part of the Book of Mosiah (8:9-19), an interview between King Limhi and a certain Ammon is recorded. Limhi was the son of King Noah and a grandson of Zeniff. Ammon was a descendant of Zarahemla. During the conversation which followed their making known to each other the positions each held, Ammon was informed that Limhi had in his possession twenty-four plates of gold filled with engravings, and some other artifacts which must have been left by a people who were destroyed long ago. Limhi asked Ammon if he could interpret an ancient language. Ammon said that he could not, but, he added, the King in Zarahemla, Mosiah, the son of Benjamin, had wherewith that he can look, and translate all records that are of ancient date. If this relates to the Urim and Thummim, as it undoubtedly does, it is evident that the two stones were no part of the treasurers of Limhi, although he had the Plates, and that King Mosiah had the sacred Instruments, or Interpreters, long before he had received the Plates to interpret.