With all due respect to Lewis, he is wrong on this point, influenced by Platonism. That view is called 'angelism', and it treats the human person as equivalent to angels. In fact, we are essentially soul-body composites. My body is not something I have, like my car. My body is part of me. To touch my body is to touch me (not all of me, of course, but nevertheless me).
I have to admit I don't know the context of his statement and only know it as a stand-alone. And as a stand-alone, it has always meant to me that the body is mortal, but the human spirit is immortal. Consequently, we should always be focused on our spiritual well-being, more so than our physical well-being.
For me, it establishes which is the owner and which is the slave. The body does not order the soul, the soul orders the body.