“The rational part of every man is supernatural in the relative sense — the same sense in which both angels and devils are supernatural. But if it is, as the theologians say, ‘born again,’ if it surrenders itself back to God in Christ, it will have a life which is absolutely Supernatural, which is not created at all but begotten, for the creature is then sharing the begotten life of the Second Person of the Deity….
“Some people use ‘spirit’ to mean that relatively supernatural element which is given to every man at his creation — the rational element. This is, I think, the most useful way of employing the word. Here again it is important to realize that what is ‘spiritual’ is not necessarily good. A Spirit (in this sense) can be either the best or the worst of created things. It is because man is (in this sense) a spiritual animal that he can become either a son of God or a devil.
“Finally, Christian writers use ‘spirit’ and ‘spiritual’ to mean the life which arises in such rational beings when they voluntarily surrender to Divine grace and become sons of the Heavenly Father in Christ. It is in this sense, and in this sense alone, that the ‘spiritual’ is always good.”
— C.S. Lewis, “On the Words ‘Spirit’ and ‘Spiritual,’ Appendix A in Miracles