Adultery is such a significant sin and so destructive to society that it is prohibited in the Ten Commandments: “You shall not commit adultery.” (NC Exo. 12:10)
In answer to a question from Peter, Christ explained about the evils in the heart of men: ” out of the heart proceed evil thoughts, murders, adultery, fornication, thefts, false witness, blasphemy. These are things which defile a man, but to eat with unwashed hands defiles not a man.” (NC Matt. 8:10)
A short time after this a group of both Pharisees and Sadducees came to demand a sign be given to them by Christ. These two groups normally conflicted with each other over religious beliefs. However, they came together to confront Christ, unified in the question they posed. Christ not only refused, but gave a principle or key it is important to understand: “A wicked and adulterous generation seeks after a sign, and there shall no sign be given unto it, but the sign of the prophet Jonah.” (NC Matt 8:15)
This key given by Christ is reliable. One of the effects of an adulterous heart is the inability to accept truth without a sign. But signs do not produce faith. Signs cannot produce faith. “And he that seeks signs shall see signs, but not unto salvation. Verily I say unto you, There are those among you who seek signs, and there have been such even from the beginning. But behold, faith comes not by signs, but signs follow those that believe. Yea, signs come by faith, not by the will of men nor as they please, but by the will of God. Yea, signs come by faith unto mighty works, for without faith no man pleases God.” (T&C 50:3)
Those with adulterous hearts require something coarse to convince them because they lack faith. When they obtain a sign and follow after it, they still do not have faith, because signs cannot produce it.
Joseph Smith commented on sign-seeking: “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.” (TPJS, p. 278, DHC 5:268; Feb. 9 1843.)
When signs attract followers, the resulting congregation of followers are all vulnerable to the sin of adultery. This is one of the reasons why so many were adulterers in Nauvoo, and later in Utah, and today among various splinter groups. It is a plague that can only be avoided by removing adulterous thoughts from the heart.
As Christ explained to Peter, it is from the heart that the evil of adultery and fornication originates. It interferes with the light required to have faith. I have consistently warned against this sin. A revelation to Joseph Smith warned: “And verily I say unto you, as I have said before, He that looks on a woman to lust after her, or if any shall commit adultery in their hearts, they shall not have the Spirit, but shall deny the faith and shall fear.” (T&C 50:4)
No adulterer is fit for Zion. The nature of that sin is to destroy families, create conflict, inspire violence, and prevent the Spirit of God from holding influence over the victims. When put outside that influence, these victims of their own lusts are open to the influence of other, false spirits. False spirits gladly minister to sign-seekers.