This promise was fulfilled. See 3 Nephi 4:8-11.
The Law which ye Shall Do. The story of the appearance of Jesus in the land of Bountiful, his ministrations and sermons, is recorded in 3 Ne. 11:1-27:12. This is the Law of the Gospel. It is the "fulness of the Gospel." It is a story that should be studied diligently and intelligently.