Having a testimony is one of the most important things a Mormon can have. They believe they receive their testimony, not through facts, but through their feelings. “As a member of The Church of Jesus Christ of Latter-day Saints, you have the sacred opportunity and responsibility to obtain your own testimony. Having obtained a testimony, you have the duty to nurture it throughout your life.
“Your happiness in this life and throughout eternity depends largely on whether you are ‘valiant in the testimony of Jesus’” (True to the Faith, p. 179).
Every testimony contains the following four parts: (1) Jesus is the true Son of God. (2) Joseph Smith was a true prophet of God. (3) The Book of Mormon is the true word of God. (4) The Church of Jesus Christ of Latter-day Saints is the true church of God. They are encouraged to “bear their testimony” as often as possible. By “bearing their testimony” they also “build their testimony.”
Also see: Revelation.