39 And after it had come forth unto them I beheld other books, which came forth by the power of the Lamb, from the Gentiles unto them, unto the convincing of the Gentiles and the remnant of the seed of my brethren, and also the Jews who were scattered upon all the face of the earth, that the records of the prophets and of the twelve apostles of the Lamb are true.
13 And it shall come to pass that the Jews shall have the words of the Nephites, and the Nephites shall have the words of the Jews; and the Nephites and the Jews shall have the words of the lost tribes of Israel; and the lost tribes of Israel shall have the words of the Nephites and the Jews.
Elder Bruce R. McConkie suggested that the records spoken of in 2 Nephi 29:12-14 would "come forth in a marvelous manner, at the direction of the president of The Church of Jesus Christ of Latter-day Saints, who is a revelator and a translator and who holds the keys of the kingdom of God on earth as pertaining to all men, the Ten Tribes included" (The Millennial Messiah, 217). We know that the Savior visited some of the lost tribes of Israel after His Resurrection and after He visited the Nephites (see 3 Nephi 16:1-3; 17:4).
Lost books are among the treasures yet to come forth. Over twenty of these are mentioned in the existing scriptures. Perhaps most startling and voluminous will be the records of the lost tribes of Israel (see 2 Nephi 29:13). We would not even know of the impending third witness for Christ except through the precious Book of Mormon, the second witness for Christ! This third set of sacred records will thus complete a triad of truth. Then, just as the Perfect Shepherd has said, "My word also shall be gathered in one" (v. 14). There will be "one fold and one shepherd" (1 Nephi 22:25) in a welding together of all the Christian dispensations of human history (see D&C 128:18).