A missionary once sat in the home of a learned scientist. The missionary tried in every logical way to convince him that The Church of Jesus Christ of Latter-day Saints was true. The scientist toyed with the missionary as a cat with a mouse, riddling the missionary's message with his superior learning. But then the missionary said something that changed the whole course of the discussion.
He said, "I know the message I am trying to bring you is true. I know it as surely as I'm here with you in this room."
The scientist was silent. He was affected by the spirit he felt in this testimony. His attitude changed. The missionary became the teacher and the scientist the learner.
Three months later the scientist knew something he had never known before. He knew that the Church was true. He was baptized and began to bear his testimony to others.