There is a quote often attributed to C.S. Lewis that goes something akin to:
"You are not a body. You are a soul. You merely have a body."
Lewis never said it, but that's beside the point. I have heard and read far too many Christians repeating this phrase approvingly, tweeting it and posting it on Facebook and otherwise passing it along as some pearl of profound wisdom. But if you're a Christian, this is bad theology. Let me explain.
When you say something like "I am a soul, I only have a body," you've split the body and soul into two different things, with the soul being the really real thing, and the body to be a mere appendage or tool, a vehicle for getting around, a spacesuit to allow the soul to temporarily survive in this alien environment. You're a ghost in a machine, as Rene Descartes would say. But is that the case? Is that what things are like?
There is a profound and obvious difference between the experience of stubbing your toe and the experience of crashing your car. Your car is a vehicle, accidental to and outside of yourself; when you crash while inside of it, you feel its impact, but when the fender crumples, you don't crumple, and you don't experience a sensation of pain along with it. And when you stub your toe, your first thought isn't, "Dang, I hope the insurance covers the damage to my toe. Is the toe repair shop open on Sundays? Should I call a toe truck?" (I couldn't resist!) No, your thought is something akin to, "OWW!!! MY TOE!!!" One is related to you; one is you.
I would guess that people are drawn to this "You are a soul" phrase because it sounds spiritual and holy and ethereal and mysterious. But such thinking actually does harm to the idea of a human being. It divides us against ourselves. It alienates us from our own bodies. It destroys our integrity.
The classic Catholic definition of the human person, as laid out by St. Thomas using the philosophy of Aristotle, maintains the distinctiveness of the soul and body while insisting on their absolute unity and dependence on each other. A person is not two substances glued together, like an arts & crafts project; a person is the combination of two principles making a natural whole, sort of like a lyric and a melody making a song. The soul is what makes this collections of organs and tissues into a living human body; a body gives the spirit a corporeal existence and makes it a human soul, as opposed to some angel-like thing. A person is an ensouled body, or an embodied soul. When a person dies, and the soul separates from the body, each is incomplete. A body without its soul is a corpse, and a soul without its body is a spirit eagerly awaiting the Resurrection.
There's an important point: denigrating the body denigrates the doctrine of the Resurrection. It's amazing how often we forget it! We think of our eternal destiny as living with God forever in heaven (ideally), but for some reason there is a tendency to think of it as a purely spiritual existence. What about the "resurrection from the dead, and the life of the world to come"? Our destiny is precisely an embodied destiny, because as human beings we are by nature embodied creatures; that will not fundamentally change at the end of time. God likes what's he done with His design of us.
There is a great moral danger hidden in the erroneous view of "You are a soul": the potential of thinking,"Well, if I really am only my soul, and my body is just a temporary husk, then what does it matter to my eternal destiny what I do with my body? Why shouldn't I eat, drink, and be merry, for tomorrow I'll simply die and be rid of this hunk of flesh? Party time! Bring on the booze and the dames!" Certain groups of Gnostics in the early Church took to this way of thinking, and promoted (or at least didn't discourage) hedonism. Don't go down that dark road, my friends.
What you do with your body affects you, because it is you who does it. You make the decision, you do the act, you suffer the consequences. You are your body, AND you are your soul, because both are required to make you. When you die, the two are separated, and pine for each other. And on the Last Day, your soul will be rejoined to your body and you will meet your eternal destiny as you, whole, once again.