This page is about the phrase "You are a soul; you have a body", and who said it. The phrase in fact comes from the 1960 novel A Canticle for Leibowitz by Walter M. Miller, Jr. (Thanks to Paul Crowley for helping track it down.) The line is as follows:
"You don't have a soul, Doctor. You are a soul. You have a body, temporarily."
(emphasis in original)
However, the phrase is often incorrectly credited to C.S. Lewis. It appears in none of his published writings, and since it conflicts with mainstream Christian belief, it is unlikely to be something he would have ever said.
All major Christian denominations believe in the doctrine of the resurrection of the body, which says that the human body is not some temporary thing but an integral part of the human whole. Therefore, the idea that a human has a body temporarily is not in accordance with mainstream Christian teaching. Indeed, the elevation of spiritual things above material things is not a mark of Christianity but of gnosticism. Lewis himself spoke against this error many times in his work:
There is no good trying to be more spiritual than God. God never meant man to be a purely spiritual creature. That is why He uses material things like bread and wine to put the new life into us. We may think this is rather crude and unspiritual. God does not: He invented eating. He likes matter. He invented it.
(Lewis, Mere Christianity)
Sometimes the phrase is quoted without the word "temporarily", reading only "You are a soul; you have a body". The word "soul" is often used to mean the human whole: body, mind and spirit. If it is used in that sense, then any objection to the phrase would be based only on quibbling about the meaning of "are" and "have". But many people misuse "soul" to mean the same as "spirit", and in that case it falls under the objections given above.
Questions or comments are welcome: thomas@thurman.org.uk.
Addendum, March 2013: There is a very similar article at Mere Orthodoxy.