Determine that you will, everyday and in every duty abolish and destroy this ruling principle of sin. it will not die unless it is gradually and constantly weakened. Spare it, and it heals its wounds and recovers its strength. Negligence allows sin to regain such power that we may never recover our former state as long as we live.
We are continually to watch out for the rising up of this ruling principle of sin and immediately subdue it. This is to be done in all that we are and do. We are to be watchful in our behaviour to others, watchful when we are alone, watchful when in trouble or joy. We are to be particularly watchful in the use of our pleasure times and in temptations.
Determine that you will no longer serve sin (Rom. 6:6). See it as the worst service of which a rational creature is capable. If you serve sin it will bring you to a dreadful end. Determine that though sin remains in you, yet you will not serve it. Remember, if the ‘old ma’ is not crucified with Christ, you are still a servant of sin, whatever you might think of yourself.
Realise that it is no easy task to mortify sin. Sin is a powerful and dreadful enemy. There is no living thing that will not do everything in its power to save its life. So sin also will fight to save its life. If sin is not diligently hunted down and dealt with by holy violence, it will escape all our attempts at killing it. It is a great mistake to think that we can at any time rest from this duty. The ruling principle of sin to be slain is in us, and so has hold of all our faculties. Sin cannot be killed without a sense of pain and trouble. So Christ compared it to ‘cutting of the right hand’ and ‘plucking out the right eye’. The battle is not against any particular lust but against all sinful lusts which war against the soul.
Mortification arising from convictions of the law leads only to dealing with particular sins, and always proves fruitless. True mortifying of sin deals with the entire body of sin. It goes tot the heart of the matter and lays the axe to the root of the tree. This is the mortification which the Holy Spirit drives the believer to do.
Mortification of particular sins arises from a guilty conscience. But mortification arising from gospel principles deals with the whole body of sin in its opposition to the renewing of the image of God in us.
John Owen (1616-83), The Holy Spirit, 167-69.