Christians: What is the purpose of the soul?

I know that death is when your soul is seperated from your body. Yet I doubt that any of you would disagree with the fact that animals can die too, even though they have no soul. Furthermore, we've known that it is the brian that is responsible for making our decisions and making us who we are. Once your neural chemistry goes south, you're not comming back. So this begs the question what is the purpose of the soul? Why do those who claim that they have been "born again" spiritually have behavioral characteristics that are indistinguishable, or even worse, than those of us who have not been born again (just look at divorce rates)?