So I find it to be a law that when I want to do right, evil lies close at hand. For I delight in the law of God, in my inner being, but I see in my members another law waging war against the law of my mind and making me captive to the law of sin that dwells in my members.
This passage explains why Christians sin. It explains why I sin so much. It is a description of the war going on right now inside of me. Every believer knows this conflict, not because we are the soldiers, but because we are the generals in both armies and we are also the battlefield!
There is a deeply rooted call to holiness that a loving Christian hears daily. The more my soul is soaked in scripture, the more I sense the call to godly living. It is what Paul calls here "the law of the mind." I know I should grow in sanctification. I know I should be like Jesus. I know sin is a bad thing for me. And I want to fight sin and gain holiness.
There is sin in me still. This sin nature (what Paul calls in this passage "the law of sin") is a serious infection of the soul. I am tempted by my own fleshly desires. I must still battle wrong and selfish urges. It is this "old man" (a term Paul uses elsewhere) that must be kept at bay by "new" teaching and commitments in Christ. My body is the battlefield where this war is waged every day. EVERY DAY. EVERY. DAY. nonstop. If this was the experience of the spiritual giant St. Paul, it has to be my day to day battle now. Understanding that is a key to beating sin.