"The spirit is willing but the flesh is weak." So said Jesus about the disciples when they couldn't stay awake. There is a consistent ontology of flesh and spirit in Scripture. Some argue about this, but I see it pretty plainly. And I think the best argument for it is that such an ontology best explains the data of spiritual formation.
If this were a philosophy paper, I'd have to get a lot more sophisticated, but I don't think we lose too much by claiming that human beings are spirit and flesh. These are not two different parts that make up one whole (the way it takes hydrogen and oxygen atoms to make water molecules). Rather, there is an essential substance (the spirit/soul/person) and a mode of its existence (human flesh).
By way of analogy (and it's only an analogy), consider the Mona Lisa. The picture to the left is the "Mona Lisa" in the medium of crayon. This is possible, because there is something that IS the Mona Lisa, and that thing can be represented in different media.
So, we might say that the thing that is me (my spirit/soul/person) is currently "represented" in human flesh. It seems possible, then, that it could be represented in something else, like a spiritual body (the soma pneumatica of 1Cor. 15).
OK, lots of objections come to mind here (Could I be "represented" in beetle flesh? No. You couldn't. Perhaps I'll get to that in another post. Am I not essentially human? Hmmm... Let's just let that sit for a bit.) The point I want to draw out is that even when I'm "born again", my spirit may be reborn, and I genuinely desire and will to do the right things, but I'm still enfleshed. And we know what flesh means: habits. God doesn't seem to take away the habits of the flesh for most of us at conversion. The good news is, we don't have to be slaves to the flesh any more, and with the assistance of the Holy Spirit we can retrain our flesh.
Whoa... too much to digest. We'll let this sit and try again tomorrow. There's really some very important stuff for spiritual formation in all this.