"For he that eateth and drinketh unworthily, eateth and drinketh damnation to himself, not discerning the Lord’s body. " (1 Cor 11: 29)
To take the sacrament when conscious of a significant sin is to be as Cain when he denied the murder of Abel. (Gen 4: 9-10) And yet--to attend the service and not take the sacrament is to accept accountability before the Lord as David did before Nathan. (2 Sam 12)
In plain English:
It's hard to come sit in sacrament meeting and not take the sacrament, possibly with family members, neighbors, or friends watching. And that's why I really believe that the brave act of passing on the sacrament tray can bring as much healing to the repentant person as taking the sacrament gives to the person with nothing so serious to repent of.