In chapter 33 of 2 Nephi, Nephi says in verse 1:
And now I, Nephi, cannot write all the things which were taught among my people; neither am I mighty in writing, like unto speaking; for when a man speaketh by the power of the Holy Ghost the power of the Holy Ghost carrieth it unto the hearts of the children of men.
I remember when I was a missionary we had some amazing experiences where the spirit communicated heart to heart between the parties involved in the discussions. As missionaries we sometimes felt like a conduit for the spirit to work though in order to touch the hearts of those we were teaching.
There is no place like a mission where I can think of a member learning this the best. In the end of the day it is the Spirit that has to make the person feel to change, not the missionary, not the Apostle, not the Book of Mormon even.