Nephi and Lehi received personal revelation as to what to say and were also given the power to say it. They were given both authority and the content. We must be spiritually prepared to receive gifts of the Spirit. The Holy Ghost often needs something to work with. We talk about being “moved” by the Spirit—the Spirit “moves” us to do something. However, we have to put something inside our hearts, minds, or souls for the Holy Ghost to move around. If you load your mind with good things, they can be brought to your remembrance in the moment you need it.
Thus, Nephi and Lehi had great success, “insomuch that there were eight thousand of the Lamanites who were in the land of Zarahemla and round about baptized unto repentance, and were convinced of the wickedness of the traditions of their fathers” (v. 19).