A sociological approach. Of course, it seems to me that believing in Christ because Christianity "works" because it fosters personal responsibility and social cohesion is utterly irrelevant to faith. If what Jesus said is true, it would not matter if Christianity failed to "work". And there is great danger in treating faith this instrumentally. If you're not careful you end up like George W. Bush, who mistakes faith for self-help and religion for politics.
I don't mean to stir up a theological dispute on a Friday afternoon, but...
If what Jesus said was "true" but Christianity nevertheless failed to "work" it would indeed matter. In fact, I would argue that the failure would be of world historical importance.
Christians believe that Jesus proclaimed a vision for the way people should both worship god and treat one another. It isn't just a declaration of how individuals should behave; it is also an instruction for how a righteous society should function. Given that Jesus was the son of god, this vision came directly from god. Thus, it is god's word. Thus, if it failed to "work" when implemented, it would mean that god's vision of and ideal world was at best flawed and at worst wrong. This would, I would think, be a Big Deal.


