In Genesis, the bible talks about this animating force. It says that God (Spirit) breathed life into the physical part of man, making us a living soul. That goes along with what I posted, from Nee's book. We are 3 parts: body (our physical shell), soul (ourselves, or inner being) and spirit (our life force and connection to God)
There's an analogy on this, that might help us see this. It's a computer analogy:
Spirit: electricity that powers the computer
I've also heard that analogy in slightly different ways. And, btw, there is some disagreement among Christians on this topic. Some people say that the soul and spirit are interchangeable. But as I said, I think the soul and spirit are two different things, and I think that is backed up by scripture.