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, emphasis added).
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.