"Persons must so live that they can enjoy the light of the Holy Spirit, or they will have no confidence in themselves, in their religion, or in their God, and will sooner or later turn from the faith."

- Brigham Young, Teachings of Presidents of the Church: Brigham Young, (1997), 41–47, Chapter 6: The Communication between God and Man
http://www.lds.org/manual/teachings-brigham-young/chapter-6?lang=eng