What would an Opeth religion be like?
Well, since the average song in the music world are 5 minutes long, and most Opeth songs are 10 minutes long, I'd say the Opeth religious services would last at least 1/2 a day if not more and would consist of one or two long "stories of life".
Instead of stained glass on the Opeth buildings, there would be windows in the design of eternity mirrors.
The stories in the Opeth bible would speak of the Virgin Melinda giving birth to baby Mikael.