Rapparee, have you read Saint Leibowitz and the Wild Horse Woman yet?
You may find that the Pope Celestine I story is parodied in the book,
although I can't be certain since I don't really know my history.

EBarnacle, your response surprises me not at all.
My first reading of the book was off-putting,
there were some passages here and there which piqued my interest
but I found the whole thing overwhelming the first time too.

For me personally,
it is a satire that improves with further reading.
Erm, mysticism?
You mean all that stuff about the dark side of the Goddess? hmmm...