Jacob clearly taught that whoredoms are an abomination before the Lord. (Jacob 2:23, 28.) The word whoredom as used here by Jacob could refer either to the sin of fornication or to the sin of adultery.
The leaders of the Church in this dispensation have been strong in condemning these types of sins. Following is an official statement published over the signatures of the First Presidency of the Church concerning this matter:
To us of this Church, the Lord has declared that adulterers should not be admitted to membership (D&C 42:76); that adulterers in the Church, if unrepentant, should be cast out (D&C 42:75), but if repentant should be permitted to remain (D&C 42:74, 42:25) and, He said, “By this ye may know if a man repenteth of his sins—behold, he will confess them and forsake them.” (D&C 58:43)In the great revelation on the three heavenly glories, the Lord said, speaking of those who will inherit the lowest of these, or the telestial glory: “These are they who are liars, and sorcerers, and adulterers, and whoremongers, and whosoever loves and makes a lie.” (D&C 76:103)
The doctrine of this Church is that sexual sin—the illicit sexual relations of men and women—stands, in its enormity, next to murder.
The Lord has drawn no essential distinctions between fornication, adultery, and harlotry or prostitution. Each has fallen under His solemn and awful condemnation.
You youths of Zion, you cannot associate in non-marital, illicit sex relationships, which is fornication, and escape the punishments and the judgments which the Lord has declared against this sin. The day of reckoning will come just as certainly as night follows day. They who would palliate this crime and say that such indulgence is but a sinless gratification of a normal desire, like appeasing hunger and thirst, speak filthiness with their lips. Their counsel leads to destruction; their wisdom comes from the Father of Lies.
You husbands and wives who have taken on solemn obligations of chastity in the holy temples of the Lord and who violate those sacred vows by illicit sexual relations with others, you not only commit the vile and loathsome sin of adultery, but you break the oath you yourselves made with the Lord Himself before you went to the altar for your sealing. You become subject to the penalties which the Lord has prescribed for those who breach their covenants with Him… .
But they who sin may repent, and, they repenting, God will forgive them, for the Lord has said, “Behold, he who has repented of his sins, the same is forgiven, and I, the Lord, remember them no more.” (D&C 58:52)
By virtue of the authority in us vested as the First Presidency of the Church, we warn our people who are offending, of the degradation, the wickedness, the punishment that attend upon unchastity; we urge you to remember the blessings which flow from the living of the clean life; we call upon you to keep, day in and day out, the way of strictest chastity, through which only can God’s choice gifts come to you and His Spirit abide with you.
How glorious is he who lives the chaste life. He walks unfearful in the full glare of the noon-day sun, for he is without moral infirmity. He can be reached by no shafts of base calumny, for his armor is without flaw. His virtue cannot be challenged by any just accuser, for he lives above reproach. His cheek is never blotched with shame, for he is without hidden sin. He is honored and respected by all mankind, for he is beyond their censure. He is loved by the Lord, for he stands without blemish. The exaltations of eternities await his coming. (Heber J. Grant, J. Reuben Clark, Jr., David O. McKay, Conference Report, October 1942, pp. 11-12.)
Also, Hyrum M. Smith reminds us that the law against adultery was one of the Ten Commandments and it is still binding upon the world:
“Thou shalt not commit adultery.” Another soul destroying crime which is very rare among the Latter-day Saints. There is no other sin, save murder only, that will so soon destroy the spiritual and moral life of men—why, it is spiritual suicide to participate in any such deadly crime. We do not sustain it; we do not suffer it; we do not tolerate it; and we do not commit it, as a people. (Hyrum M. Smith, Conference Report, October 1906, pp. 44-45.)