Simple. There is the universal Catholic Church anchored in sacred scripture, tradition, and revelation and the rest is all manure as history has shown.
The Inquisitors were the thought police.
The writer himself was a Catholic priest, and part of "The Holy Office"...and was able to pour over volumes now lost to history. At the Vatican, no less.
The man had freedom to study in the library there for some years. Though the work may not be perfect in all ways, it cannot simply be dismissed as "manure". If we are to consider what "history has shown" we mustn't so quickly dismiss the sort of information brought to us here on this thread, in post #43 & somewhat re-iterated in #45.
Al else, claims to the contrary are manure, indeed AS HISTORY HAS SHOWN.