Words of Mormonby Eldin Ricks
Mormon was at work on his abridgment of the large plates of Nephi 1 when he discovered the small plates of Nephi, a prophetic record from early Nephite history (W of M 1:3). Because he was deeply impressed with the messianic prophecies that he read on the small plates, and in response to "the workings of the Spirit," Mormon included that set of plates with his digest (W of M 1:4-7). But because that record ended a few years before the book of Mosiah began (c. A.D. 130), Mormon assumed the prerogative of an editor and appended this historical postscript to the small plates to bring its conclusion into correlation with the opening of the book of Mosiah. This appendage, called the Words of Mormon, was composed about A.D. 385.