Dr. Henry Morris, in the New Defender’s Study Bible, gives this comment on verse 14: “The ‘natural’ man, still unsaved, cannot appreciate spiritual truths. He must first understand Christ’s atoning sacrifice for him, but even that is ‘foolishness’ to him (1:18) until the Holy Spirit Himself convicts him of its reality (John 16:7-11).” Basically, the “natural” man is one who does not have the Holy Spirit residing within him. As Jesus said, “Flesh gives birth to flesh, but the Spirit gives birth to spirit” (John 3:6). Read more: http://www.gotquestions.org/natural-man.html#ixzz3Te4YMPAY