Matthew 16-17

Matthew 16:4
Elder Neal A. Maxwell (1926–2004) of the Quorum of the Twelve Apostles explained why it is that “a wicked and adulterous generation seeketh after a sign” (Matthew 16:4): “Why does this generation seek a sign? queried Jesus with a deep sigh. (See Mark 8:12.) The more wicked and adulterous the people of a particular period, the more they demand signs as a condition of belief. Sensual individuals crave and live by sensations. Disciples, instead, walk and ‘overcome by faith’ (D&C 76:53), accepting gratefully the evidence of things not seen which are true (see Heb. 11:1; Alma 32:21)” (“Answer Me,” Ensign, Nov. 1988, 31–32).

Matthew 16:13-17
President Dieter F. Uchtdorf of the First Presidency taught that faith in Jesus Christ should be the core of our testimony and that this testimony must come to each person through individual revelation:
“We cannot depend on the testimonies of other people. We need to know for ourselves. President Gordon B. Hinckley said, ‘Every Latter-day Saint has the responsibility to know for himself or herself with a certainty beyond doubt that Jesus is the resurrected, living Son of the living God’ (‘Fear Not to Do Good,’ Ensign, May 1983, 80).
“The source of this sure knowledge and firm conviction is divine revelation. …
“We receive this testimony when the Holy Spirit speaks to the spirit within us. We will receive a calm and unwavering certainty that will be the source of our testimony and conviction irrespective of our culture, race, language, or socioeconomic background. These promptings of the Spirit, rather than human logic alone, will be the true foundation upon which our testimony will be built.
“The core of this testimony will always be the faith in and the knowledge of Jesus Christ and His divine mission” (“The Power of a Personal Testimony,” Ensign or Liahona, Nov. 2006, 38).

Matthew 17:20 Faith to Move Mountains
Bishop Richard C. Edgley of the Presiding Bishopric spoke about other kinds of “mountains” that can miraculously be moved by the exercise of faith: “I have never witnessed the removal of an actual mountain. But because of faith, I have seen a mountain of doubt and despair removed and replaced with hope and optimism. Because of faith, I have personally witnessed a mountain of sin replaced with repentance and forgiveness. And because of faith, I have personally witnessed a mountain of pain replaced with peace, hope, and gratitude” (“Faith--the Choice Is Yours,” Ensign or Liahona, Nov. 2010, 33).