It is always dangerous to assert an essence of anything so sprawling, diverse and multiple as Christianity, which is an institution, or a tradition, or a body that has always been as much at war with itself as with any of the others against which it constitutes itself. But it is perhaps close enough to something like the truth to suggest that, somewhere near the heart of this monstrous body, this (un)holy city, is a problem that can be set out something like this: Jesus Christ died for our sins. Perhaps that sounds less like a problem than a solution; but the devil is, as always, in the details.