That one's a metaphor for the expungement and atonement of sin...
Part of recovery is to think a little more abstractly there...
I'm not surprised Mormons have issues understanding that one; there isn't much available for "rituals" in this department (if you don't lie to the bishop on those interviews, you're gonna come out feeling a lot worse afterwards than before you went in).
That's an outgrowth of the Calvinist/Puritan New England culture (JS and BY did grow up in that part of the country).
SLC Perhaps gonna "go Injun" on this one... Native Americans have some really nice rituals on this one... Then there was the time I ran into a "born again," who was always shoplifting... He figured if he got away with it, it was God's will and he needn't feel guilty...
It is from the Bible, Revelations 7:14. Blood = Jesus' death. White = innocent, forgiven. Divine beings, like angels, are often said to appear in white apparel.
If I had been the publishing editor for the Bible, I would have suggested that the author should reconsider the metaphor "white in the blood".