I had only traveled a short time to testify to the people, before I learned this one fact, that you might prove doctrine from the Bible till doomsday, and it would merely convince a people, but would not convert them. You might read the Bible from Genesis to Revelation, and prove every iota that you advance, and that alone would have no converting influence upon the people.
Nothing short of a testimony by the power of the Holy Ghost would bring light and knowledge to them—bring them in their hearts to repentance. Nothing short of that would ever do. You have frequently heard me say that I would rather hear an Elder, either here or in the world, speak only five words accompanied by the power of God, and they would do more good than to hear long sermons without the Spirit. This is true, and we know it.
(Brigham Young, Discourses of Brigham Young, p. 330)