Sentence:  He may not be able to become a pagan or a Chaldean, but he can become—however partially and reluctantly—a <WSD>Patmosian</WSD>, since the Apocalypse of St. John of Patmos was indeed a significant part of the “creed” in which as a child he was "suckled". 
Meaning of the word marked with <WSD> tags:  A believer in Saint John's apocalyptic vision.