The convincing power of the Holy Ghost

"The convincing power of the Holy Ghost is so great that there can be no doubt that what He reveals to us is true.

President Joseph Fielding Smith said:
“When a man has the manifestation from the Holy Ghost, it leaves an indelible impression on his soul, one that is not easily erased. It is Spirit speaking to spirit, and it comes with convincing force. A manifestation of an angel, or even of the Son of God himself, would impress the eye and mind, and eventually become dimmed, but the impressions of the Holy Ghost sink deeper into the soul and are more difficult to erase” (Answers to Gospel Questions, comp. Joseph Fielding Smith Jr., 5 vols. [1957–66], 2:151).
President Smith also said, “Through the Holy Ghost the truth is woven into the very fibre and sinews of the body so that it cannot be forgotten” (Doctrines of Salvation, comp. Bruce R. McConkie, 3 vols. [1954–56], 1:48)."  (From Gospel Principles “Chapter 7: The Holy Ghost,” Gospel Principles, (2009),31–33)