Words of Mormon 1:5-7
“It appears the large plates of Nephi were kept and expanded by the kings, but the small plates of Nephi were kept by the prophets, and were not expanded… . The first important change that took place at the time of King Benjamin was that the small plates of Nephi became full, and this separate spiritual record was given to King Benjamin for safe keeping (Omni 1:25)… . A second important change during the time of King Benjamin was that the large plates of Nephi were now used to record both secular and spiritual events. There was no longer a separate spiritual record being kept; therefore preachings, visions, and prophecies, etc., were included in the large plates.” (Rex C. Reeve, Jr., First Nephi, The Doctrinal Foundation, BYU Religious Studies Center, p. 106)