refer in this text to 1 Ne. 6; 1 Ne. 9; Words of Mormon 1:5-7
“When the family of Lehi reached the western hemisphere, Nephi was commanded of God to make a set of plates upon which the history of his people was to be kept. He did so, recounting their journey in the wilderness and prophecies he and his father had made. This record is known to us as the large plates, which apparently contained the book of Lehi. Some twenty years later (ca. 570 B.C). Nephi was commanded to make another set of plates known to us as the small plates or book of Nephi (see 2 Nephi 5:28-31), in which he recorded only that which was sacred. Thus the book of Lehi became primarily a temporal history, while the book of Nephi became a record of prophecies and a collection of sacred events.” (R. Millet and J. F. McConkie, Doctrinal Commentary on the Book of Mormon, 1:145)