This is a very important chapter. It contains the promise of the Lord that if the modern Saints appreciate the abbreviated version of the Book of Mormon which we now have, there will be other things added from time to time. The Lord refers to these as "the greater things."
These verses imply that Jesus may have given the Nephites more scriptures which had been given to Lehi after he left Jerusalem. In any event, whatever the Nephites received, Jesus now expounded extensively to make certain that the people understood them.