The natural man refers to someone who hasn't been saved and therefore doesn't have the dwelling holy spirit.People in this condition reject the gospel massage and view it as foolishness,grace,and salvation don't make sense to them and and don't have personal value.They don't have interest,understanding,trust or appreciation for Christ and his word because they haven't had the work of God's spirit in their hearts.Christ word must be understood on a spiritual level,not just an intellectual level
Those who has ears must listen and do what's right in front of our almighty.