For the Christian, we have a new life and a new identity. We are not who we once were. In Jesus Christ, we died to our old way of life and have been raised to walk in newness of life. When sin crouches at your door, remind yourself that this is not who you are anymore. By the power of the Spirit, refuse to live in that for which your Savior died. Resolve to never live in the sins that defined you before you were in Jesus.
Early in my Christian life, I heard the famous quote from the English pastor and theologian John Owen, “Be killing sin or it will be killing you.” While that quote may sound a little radical, for any person who truly knows himself, he understands that his sin can kill him. He feels in his bones the havoc that sin reeks on his joy, his walk with the Lord, his relationships and his witness.
Dealing with our own personal sin also shows us that no superficial adjustments in our lives will bring about real progress. Our sin is deep-rooted and resists fixes that are merely ornamental. To really kill our sin, we must get down to the root of it.
Because this work is hard, our flesh resists it. So, what our souls need are overwhelming reasons that drive us to deal with the root of our sins and grow into the likeness of Christ. Paul provides the fuel our souls need for the war with sin in Colossians 3:5-11. (I’m also including verses 1-4 for context.) In writing to this congregation that was fighting with a mixture a legalism and pagan mysticism, Paul provides the compelling logic that helps us to understand why we need to make war against our sin.
 If then you have been raised with Christ, seek the things that are above, where Christ is, seated at the right hand of God.  Set your minds on things that are above, not on things that are on earth.  For you have died, and your life is hidden with Christ in God.  When Christ who is your life appears, then you also will appear with him in glory.
 Put to death therefore what is earthly in you: sexual immorality, impurity, passion, evil desire, and covetousness, which is idolatry.  On account of these the wrath of God is coming.  In these you too once walked, when you were living in them.  But now you must put them all away: anger, wrath, malice, slander, and obscene talk from your mouth.  Do not lie to one another, seeing that you have put off the old self with its practices  and have put on the new self, which is being renewed in knowledge after the image of its creator.  Here there is not Greek and Jew, circumcised and uncircumcised, barbarian, Scythian, slave, free; but Christ is all, and in all. (ESV)