Well, lets get back to the topic of Cal. In the novel he seems to be religious in terms of "going to church", oftentimes religion is referenced in his thought process. His actions on the other hand do not seem to be influenced majorly by his belief in one special kind of god in some special kind of way. I'd definitely agree with Jonas and say that the motives have a rather political than religious basis.
In the Northern Ireland conflict the two confessions, Catholics and Protestants have developed into political parties, the Nationalists and Loyalists.
Didn't that happen because the Irish were mainly Catholic and the British "invaders" mainly protestant? I believe so. That would at least explain the "policizied" confessions of Christianity.