"The idea of sin eating was simple: someone was hired to “eat” another person’s sins. As a person lay dying, someone would place a piece of bread on his or her chest, which would “absorb” that person’s sins. However, where would that person’s sins go to after that? After all, bread only lasts for a few days at best. A local pariah, known as the sin eater, would come and eat the piece of bread, thereby “eating” the deceased person’s sin. The person who died would go to heaven, and the sin eater would get paid for his or her services."
Essentially, the sin eater traded his or her own soul in exchange for the bit of money earned by sin eating. He or she would absorb the sins of so many people that eternal damnation was assured. This concept was not the only example during the Middle Ages and beyond of people who traded their souls for material gain; the Faustian legend is about a man who sold his soul to the devil for another year of life on earth. Witches were believed to sell their souls to the devil in exchange for magical powers. What set the sin eater’s exchange apart was that he or she was able to allow another person to enter heaven."
this job was literally the worst job in human history