To mortify something is to kill it. In biblical usage we are told to “mortify our members”, or to “put to death the members of our flesh”. That is, put to death those parts of our self that are opposed to God. Thus we read to “crucify our flesh”, “resist sin”, “don’t yield our members as instruments of unrighteousness” and “put off the old man”.
The first thing to realize is that mortification of the lower nature does not remove the lower nature from the person. It is not “death” in the sense that this part of us is annihilated and ceases to exist. It means that we are free from its rule. We still must suffer it though, feeling wrong desires, thinking wrong thoughts and experiencing the pressure of temptation.
That is, before conversion we were under the rule of sin. We could not help but do wrong. With time in fact we got worse. After being born again we have the power and ability to resist sin and “put on the new man” and prevent sin from ruling us as before. Even though victory over sin is part of the atonement the transition to a new life is not instantaneous, automatic or easy. Those who expect an easy road to holiness are soon disappointed by their seeming lack of power over their sin nature; even though they want to obey and believe they are a new person in Christ.
First, we need to realize and admit that crucifixion is a slow and painful death. It hurts to die. When we resist the evil within us we have to fight a painful battle. For one thing we must resist temptation. When we refuse to act on our desires and impulses it is a painful process. That is, resisting illicit desire takes energy. To refuse pleasure is to accept pain. It is hard work that is often intense and prolonged. Mortification is a process not an act and we must progressively and continually put to death our lower nature. This process is often humiliating and always painful.
Second we must learn that even though we are using our will to resist sin we cannot depend on it. To attempt mortification by mere will power is to fall into the snare of legalism. In fact, the failures encountered in pursuing a life of holiness are allowed in order to teach us to not depend on ourselves. If failure is honestly admitted before God and men then we can get “grace to help in time of need”. That is, as we realize we cannot obey God just because we want to and try to then we can begin to gain power over sin. There are multiple components to this dependence on God. For one thing we cannot fight sin by merely focusing on it and resisting it. We must turn from sin to God; not just from sin. We need to feed the higher nature. “Walk in the Spirit and you will not fulfill the desires of the flesh” sums this up. Placing our attention on God, seeking Him in prayer, being active in the building up of His body and His kingdom will do much to mortify sin. Another powerful weapon in our war against sin is gaining revelation through the bible. For example, when a person actually sees that they are already freed from sin by the work of Jesus then they can resist sin much easier. That is, they appropriate the power over sin by faith. That is why Paul said to “reckon yourselves dead to sin”. On a more mystical note it is possible, through contemplation, to have direct experiences with God and to have Him reveal the spirit behind a temptation. When the choice is between two beings, one infinite and lovely and one finite and ugly, the ability to resist sin is greatly enhanced.
It is said of Jesus that “for the joy set before him he endured the cross”. We too can gain energy for the battle by seeing the reward. The fruit of righteousness is life and peace. Mortification leads to joy and peace. The outcome of resisting sin and drawing close to God is the reward of a resurrected life. This life is stimulating, liberating, creative, and fulfilling. There is a price to pay for mortification but the reward is worth it.