The Lord has said that “an evil and adulterous generation seeketh after a sign” (Matthew 12:39). Those who desire a sign without first exercising faith reveal their spiritual condition.
The Prophet Joseph Smith gave a modern example of this principle: “When I was preaching in Philadelphia, a Quaker called out for a sign. I told him to be still. After the sermon, he again asked for a sign. I told the congregation the man was an adulterer; that a wicked and adulterous generation seeketh after a sign; and that the Lord had said to me in a revelation, that any man who wanted a sign was an adulterous person. ‘It is true,’ cried one, ‘for I caught him in the very act,’ which the man afterwards confessed, when he was baptized” (History of the Church, 5:268).
President Joseph F. Smith (1838–1918) explained the weakness of requiring a sign to uphold faith: “Show me Latter-day Saints who have to feed upon miracles, signs and visions in order to keep them steadfast in the Church, and I will show you members of the Church who are not in good standing before God, and who are walking in slippery paths. It is not by marvelous manifestations unto us that we shall be established in the truth, but it is by humility and faithful obedience to the commandments and laws of God” (in Conference Report, Apr. 1900, 40).