The promise given in Doctrine and Covenants section 17 was that the three witnesses of the Book of Mormon—Oliver Cowdery, David Whitmer, and Martin Harris—would have the privilege of viewing precious treasures of the Nephite and Jaredite civilizations: plates, breastplate, sword of Laban, the Urim and Thummim, and miraculous directors (“Liahona”). Each of these ancient relics is mentioned in the Book of Mormon as being of great worth and as passing from one generation to another.

Let us example briefly what is known about the ancient relics.

Plates. The Book of Mormon is a sacred record of peoples in ancient America engraved upon metal plates. There are two kinds of Nephite plates—small and large. The small plates are devoted to spiritual matters such as the ministry and teachings of ancient prophets. The large plates are a mixture of spiritual and secular history of the ancient peoples. The Plates of Mormon are an abridgment by Mormon from the large plates of Nephi. These plates contain a continuation of the history by Mormon and his son Moroni. The Plates of Ether contain a history of another ancient civilization—the Jaredites. The Jaredite record was abridged by Moroni.

Breastplate. There are two types of breastplates mentioned in scripture: (1) the front part of a soldier’s protective clothing or armor, symbolically portrayed as a breastplate of righteousness (Isaiah 59:17; Ephesians 6:14) and (2) an article of linen clothing with twelve precious stones worn by the high priest under the law of Moses (Exodus 28:13–30; 39:8–21). The breastplate used in the translation process of the Book of Mormon is spoken of in conjunction with the Urim and Thummim.

Sword of Laban. The sword of Laban was used by Nephi to slay Laban. According to Nephi, the sword “was of pure gold, and the workmanship thereof was exceedingly fine, and I saw that the blade thereof was of the most precious steel” (1 Nephi 4:9). Nephi and King Benjamin wielded the sword of Laban in defense of their people.

Urim and Thummim. Urim and Thummim is a Hebrew term meaning “Lights and Perfections.” It is an instrument for obtaining revelation from the Lord and translating languages (see Exodus 28:30; Leviticus 8:8; Numbers 27:21; Deuteronomy 33:8; 1 Samuel 28:6; Ezra 2:63; Nehemiah 7:65; Joseph Smith—History 1:35). Using the Urim and Thummim is the prerogative of a seer. As a seer, Joseph Smith used the Urim and Thummin in translating the Book of Mormon and in obtaining revelations from God.

Liahona. At the door of Lehi’s tent was a ball of curious workmanship known as the Liahona. The ancient relic guided Father Lehi’s family to the Promised Land. The word Liahona has been interpreted to mean “to God is light” and “of God is light.