Plate from ‘The Art of Living Well, and of Dying Well’, from the Library of Congress
The Black Death had a significant impact on the church. The priesthood suffered as many deaths as any other part of society: of the 600 bishops, 230 died during the plague, 13 “disappeared” and there are 20 who cannot be accounted for. These senior clergymen would have been relatively isolated by comparison with the huge majority of the priests. They were expected to give last rites and hear a final confession for the dying, which meant being exposed to the disease. It reached the point that the priests simply refused to visit the sick, which would have been a real problem for a deeply religious culture: without a final confession, would they miss their place in the afterlife?
To make matters worse, the lost priests needed to be replaced, and to do that the church had to lower their standards. They ordained many people who would have been passed over in the past, people who had limited understanding of the faith they represented. And, of course, this compounds the problem of having so many people dying: more people than ever needed last rites, but if you actually managed to get a priest to visit they may not know what needs to be done.
People had to take matters into their own hands, and to do that they needed instructions on what was expected. To fill that need came the Ars Moriendi, the Art of Dying. These were books that set out what a dying person should do, what temptations they should resist, what prayers they should make to give them passage into heaven.
Devils tempt a dying man with crowns, via Wikipedia
These books were particularly popular with the growing middle-class, who could both read and afford to buy the book. The advice in the books may also have become part of the noblesse oblige, the duty that the lords had to care for their serfs. In the absence of priests, it was the responsibility of a lord to guard his serfs’ souls. The church didn’t exactly sanction these texts and they weren’t responsible for making them. After all, the church wasn’t known for giving away something that kept them important in their society.
Suppose in your game world that the dominant religion has been struck by a catastrophe, something that prevents them from aiding all of their faithful. The gap is filled by unofficial books of religious instructions. Perhaps these books are incorrect, even malicious – what if they were written to deceive people and that by following them they are participating in something terrible?
[You can see more about the Ars Moriendi in this paper at the University of Ottawa]