I'm an MA in philosophy. You can't go wrong by writing on the mind-body problem. In other words, the body is a physical entity presumably subject to the laws of physics. Unless the mind is itself a physical epiphenomenon (in which case the idea of soul or spirit goes out the window), how in the world does a noncorporeal, nonphysical entity control a physical object like the human body? And if there is no such thing as a soul or mind, how can the physical body be held responsible for its actions?
Google will have TONS of stuff on this problem, but here's a good place to start:
http://www.wikipedia.org/wiki/Mind-body_problem