nah, religion doesn't help that much.. things like The Holy Graal ain't only a religious term, but are also related to legends and myths like this one bout King Artur.
Last Supper - you don't have to be religious fanatic to know it.. a bit of history of art would be enough
this guy in square and circle - Vitruvian Man (sorry, don't know it's english name) but it's the same thing as with Last Supper..
Mary Magdalene [or whatever] - well.. this may be complicated for people who umm.. let's say aren't 'interested' in the topic. but you can always check wikipedia or somethin like that to get it.
what's more.. umm.. don't remember the book that well, but same goes to Opus Dei and all the stuff like symbols V and /\..
