In the film, "The Order" why does the film have so many important events occuring in St. Peter's?

Answer 1

Because that is the place which constitutes the source of authority of the vatican. St Peter's is like the white House of the U.S, if the movie is dealing with such an issue as sin eaters, then that is the place where such a notion is completely killed.

Dont 4get that the sin eater's brother died in St Peters as it was being constructed.