In 2 Nephi 27:12–13, Nephi foresaw that the plates of the Book of Mormon would be “hid from the eyes of the world” and that “the eyes of none shall behold it save it be that three witnesses shall behold it, by the power of God” and “none other … shall view it, save it be a few according to the will of God.” Here in Ether 5:2–3, Moroni reaffirmed that the plates will be shown by the power of God to three of the people who had assisted in bringing forth the plates to verify the truth of the work. In Ether 5:4, Moroni is quoting, either of himself or through the Lord, the ancient Hebrew law of witnesses, in which two or three witnesses were required in establishing the truth of important testimonies in court. Deuteronomy 19:15 says: “One witness shall not rise up against a man for any iniquity, or for any sin, in any sin that he sinneth: at the mouth of two witnesses, or at the mouth of three witnesses, shall the matter be established.” Moroni said, “In the mouth of three witnesses shall these things be established” (Ether 5:4).
This is followed by a statement that “the Father, and the Son, and the Holy Ghost bear record—and all this shall stand as a testimony against the world at the last day.” Moroni knows that he has no one else that he can call on to validate the truthfulness of the record he is giving here in the book of Ether. So, he calls these three Heavenly witnesses to corroborate that his record is true. Likewise, in Doctrine and Covenants 6:28, the Lord affirmed the validity of this law of witnesses, declaring in April, 1829, that “in the mouth of two or three witnesses shall every word be established.” Witnesses, together with physical and written evidences, still play crucial roles in religious life, as well as in legal systems throughout the modern world, in coming to recognize and know the truth.
Book of Mormon Central, “Why Were Three Key Witnesses Chosen to Testify of the Book of Mormon? (Ether 5:4),” KnoWhy 267 (January 27, 2017).