What is a testimony good for?

A testimony provides proper perspective, motivation, and a solid foundation on which to build a life of purpose and personal growth. It is a constant source of confidence, a true and faithful companion during good times and bad. A testimony provides us with a reason for hope and gladness. It helps us cultivate a spirit of optimism and happiness and enables us to rejoice in the beauties of nature. A testimony motivates us to choose the right at all times and in all circumstances. It motivates us to draw nearer to God, allowing Him to draw nearer to us (see James 4:8).

(Dieter F. Uchtdorf, “The Power of a Personal Testimony,” Ensign, Nov 2006, 37–39)