I don't believe in Christianity primarily because of the brain

[Crossless2.0]

I agree with Rob that, lacking a rigorous definition of the word, 'soul' is best understood as a metaphor. As such, I wouldn't ordinarily have a problem with its use, except that most people don't seem to use it as a metaphor and their sense of the word is too slippery and imprecise to latch onto without confusion on both sides in most conversations.