According to Lee Donaldson, the fifth element of ancient covenants deals with witnesses. In Ether 2:9, Moroni makes the statement, "and now, WE can behold the decrees of God concerning this land."
The prophet Ether personally stood as an eyewitness to the terrible fulfillment of the curses of the covenant and "beheld that the words of the Lord had all been fulfilled; and he finished his record" (Ether 15:33). However, a broader look at the Book of Mormon reveals that this same covenant to serve Jesus Christ as the God of this land is also part of the plates of Nephi and the plates of Mormon (see illustration). Why is this same covenant given in all three sets of plates? Is it significant that the Lord selected three different sets of plates to establish his covenant? And is this the reason why Mormon wanted the message of the plates of Ether to be included with his record? (Mosiah 28:19).
Having a set of three in making covenants is an ancient pattern. For instance, the baptismal covenant is made "in the name of the Father, and of the Son, and of the Holy Ghost" (3 Nephi 11:25). Moroni, in the middle of his abridgment of the Jaredite record, prophesies that "in the mouth of three witnesses shall these things be established; and the testimony of three . . . shall stand against the world at the last day" (Ether 5:4). [Lee L. Donaldson, "The Plates of Ether and the Covenant of the Book of Mormon," in The Book of Mormon: Fourth Nephi through Moroni, From Zion to Destruction, pp. 72-74] [See the commentary on Ether 5:4]