Messages of the First Presidency, October 1942, 6:170-185; “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.” – James R. Clark
Proverbs 6:16-19; “These six things doth the LORD hate: yea, seven are an abomination unto him: 17 A proud look, a lying tongue, and hands that shed innocent blood, 18 An heart that deviseth wicked imaginations, feet that be swift in running to mischief, 19 A false witness that speaketh lies, and he that soweth discord among brethren.”
Let’s take a look at some of these seven abominations –
rum is the Hebrew word for proud. It means to be highly active to rise or raise, bring up, exalt oneself, lofty.
sheqer is Hebrew for untruth by implication a sham, falsehood, liar, vain
charash is Hebrew for deviseth. It means to scratch, engrave, fabricate, devise (in a bad sense) to be silent, let alone, be deaf…
‘aven is Hebrew for wicked and it means to pant or exert oneself usually in vain, strictly nothingness, also trouble, vanity, wickedness, idol, evil…
machashabah is Hebrew for imaginations and it means a contrivance, intention, plan (whether bad, a plot, or good, advice) – cunning work, curious work, device…
So nowhere in those verses do we see that sexual sin is next to murder. What we do see is that God hates the shedding of innocent blood, and those who go about devising plans and evil lies.
We might imagine that sexual sin could be the reference of running into mischief, but as detailed as the other Hebrew words are it’s more speculation than fact. Matthew Henry observed this is meant as an envious, revengeful plot for greed and selfishness. Running swiftly into sin is referencing those who are quick to judge and too greedy for the reward of shaming others.
It’s difficult at best to determine exactly what defines sexual sin in Mormonism. They say it’s adultery yet they’re polygamists, so if adultery, i.e. having an affair outside the women or man you’re married to, is the sin next to murder, Joseph Smith committed that very sin. He married other men’s wives while they were away on missions.