The theological argument of the previous passage was precise: the person baptized into Christ has died to sin and been raised to newness of life. Now Paul moves from what is true to what therefore must be done — from the indicative to the imperative, as careful readers of Paul have always noted. What God has declared to be the case in Christ, the Christian must act as though it is the case. Because it is.

"Therefore do not let sin reign in your mortal body so that you obey its lusts" (Romans 6:12).

This is a command, not a description. Paul is not saying that sin will automatically fail to reign in the Christian. He is commanding the Christian not to allow it to reign. The dead-to-sin reality he established in verses 1–11 does not remove the need for decision and resistance. It provides the ground from which resistance becomes possible and meaningful. A person who has never been freed from slavery cannot be commanded to stop serving the master. But a person who has been freed can be commanded — and must be.

The instruction has a positive counterpart: "and do not go on presenting the members of your body to sin as instruments of unrighteousness; but present yourselves to God as those alive from the dead, and your members as instruments of righteousness to God" (Romans 6:13).

The body — hands, eyes, tongue, feet, mind — is the field of this battle. Paul is not describing an interior spiritual struggle disconnected from the physical. He is talking about what a person does with their actual body. The same body that could be offered to sin as an instrument is to be offered to God as an instrument. The same hands that could do wrong are to be used for what is right. The same tongue that could wound is to be used for what builds up. The physics of the matter are direct: a life of righteousness requires the active, daily presenting of one's self to God.

What gives this command its traction is the basis Paul gives for it: "For sin shall not be master over you, for you are not under law but under grace" (Romans 6:14).

This verse has been misread to mean that because we are under grace, the moral demand is lightened. Paul means precisely the opposite. The law demanded righteousness and provided no power to produce it. It exposed sin and measured the distance between the sinner and what God required, but it could not close that distance. Grace is not a lighter version of the law's demand — it is the power that law never had. Being under grace means being in a system where God has acted to secure the victory over sin that law-keeping could never achieve. The Christian is not under a set of rules he must fulfill through willpower. He is under the reign of a risen Lord who broke sin's power at the cross.

Sin shall not be master — not because the Christian is strong enough to overcome it alone, but because Christ overcame it, because the Christian has been united with that victory at baptism, and because the grace under which he now lives is the operative power of a God who raised the dead. The command to present oneself to God is an invitation to live out of that reality — to act in accordance with what is already true.

Three verses. One command, one positive alternative, one reason. Paul moves quickly here because the logic is tight and the application is plain. The person who has been buried with Christ and raised in Him does not belong to sin anymore. The body that was once sin's instrument is now God's instrument. Living accordingly is not an aspiration. It is the appropriate response to what has actually happened.