"But I shall make an account of my proceedings in my days. Behold, of my father, upon plates which I have mad with mine own hands; wherefore, after I have abridged the record of my father then will I make an account of mine own life."
Nephi, with the guidance of the Lord, made an abridgment for those in the future to read of Lehi's works and visions. This is to the 116 pages mentioned before could still be a part of the Book of Mormon, but that Satan could not fulfill his design of destroying the credibility of the Book of Mormon. The fullness of history and such were kept separately for the sake of keeping the sacred things just that, sacred. This will be explained more later, as Nephi speaks of it later.