“An unregenerate man may do something like mortification, but the real work itself, so that it may be acceptable with God, he can never perform. Some of the Philosophers declare how they have conquered the world and self, and are able to regulate their passions and affections! The lives however of most of them reveal their boasts differ from true mortification just as the sun which is painted on a fence differs from the sun itself; it has neither light nor heat. There is no death of sin without the death of Christ. You realize how the Papists, in their vows and penances seek mortification according to the principles of their church, yet they are like Israel who, seeking for their own righteousness, have not attained it! Why? Because they seek it by works of the law and not by faith (Romans 9:31-32).
– John Owen, The Mortification of Sin, p.41