Sentence:  But Michael Sept had unmasked him , revealing he had never been a bishop , but was an Anabaptist , afraid to state his faith , because he <WSD>knew</WSD> John Calvin had written a book against their belief that the soul slept after death . 
Meaning of the word marked with <WSD> tags:  be cognizant or aware of a fact or a specific piece of information; possess knowledge or information about