You're right that the spiritual meaning of "passion" is "suffering", directly from the Latin. The adjective, like you say is "passionate" but I have never heard it used in connection with the meaning of "passion" as "suffering". Given what you say about the content of both books and the fact that the author is the same, it is quite likely that "passionate" here has the meaning of "relating to suffering".
Unless you made the religious context really clear, nowadays, people would automatically think that "passionate" meant "enthusiastic, committed etc" or alternatively "amorous, romantic".