Neal A. Maxwell
"…the splendid Book of Mormon advises that a third scriptural witness is yet to come from the lost tribes (see 2 Nephi 29:12-14). Its coming is likely to be even more dramatic than the coming forth of the second testament. Those who doubt or disdain the second testament of Christ will not accept the third either. But believers will then possess a triumphant triad of truth (see 2 Nephi 29:12-14). Were it not for the Book of Mormon, we would not even know about the third set of records!
"We do not know when and how this will occur, but we are safe in assuming that the third book will have the same fundamental focus as the Book of Mormon-'that . . . their seed [too] ... may be brought to a knowledge of me, their Redeemer' (3 Nephi 16:4). If there is a title page in that third set of sacred records, it is not likely to differ in purpose from the title page in the Book of Mormon, except for its focus on still other peoples who likewise received a personal visit from the resurrected Jesus (see 3 Nephi 15:20-24; 3 Nephi 16:1-4).
"Thus, in the dispensation of the fulness of times there is not only a 'welding together' (D&C 128:18) of the keys of all the dispensations, but there will also be a 'welding together' of all the sacred books of scripture given by the Lord over the sweep of human history. Then, as prophesied, 'my word also shall be gathered in one' (2 Nephi 29:14). Then there will be one fold, one shepherd, and one stunning scriptural witness for the Christ!" (Book of Mormon Symposium Series, First Nephi, edited by PR Cheesman, MS Nyman, and CD Tate, Jr., 1988, p. 15)