What then? Are we to sin because we are not under law but under grace? By no means! Do you not know that if you present yourselves to anyone as obedient slaves, you are slaves of the one whom you obey, either of sin, which leads to
death, or of obedience, which leads to righteousness? But thanks be to God, that you who were once slaves of sin have become obedient from the heart to the standard of teaching to which you were committed, and, having been set free from
sin, have become slaves of righteousness. I am speaking in human terms, because of your natural limitations. For just as you once presented your members as slaves to impurity and to lawlessness leading to more lawlessness, so now present your members as slaves to righteousness leading to sanctification. (Romans 6:14-19 ESV)
This text is serious encouragement for the believer who for the moment feels defeated by the constant nag of besetting sins. God’s promise here is very clear … “sin will have no dominion over you.” I appreciate how John Piper expounds this truth. He states:
Now [the] question is: Why does being "under grace" guarantee that sin will not master us? Notice the logic of verse 14: "Sin shall not be master over you, for you are not under law but under grace." This is a promise: "Sin shall not be master over you." It is not a command like "Thou shalt not kill." It is a promise of what must be and will be for all who are
under grace. We can tell this because verse 14 is given as the basis of a command in verse 13: "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." That's a command. Now verse 14 adds the reason: "For sin shall not be master over you."
This is the striking way that New Testament ethics is structured. "Don't let sin master you, because sin is not going to
master you." If that strikes us as strange, which it does at first, it's because we come to the Bible with our man-centered bias toward self-determination. In other words, we come with the bias that if the Bible tells us to make a choice
(like "don't present your members to sin"), then in the moment of that choice we, not God, have the final say. And if you come with that bias – that genuine, responsible choice means ultimate self-determination – the connection between
verse 13 and verse 14 will probably make no sense. Don't yield to sin (verse 13) because sin will not be master over you (verse 14).
But if you learn from Scripture to see the sovereignty of God and the real responsibility of man in such a way that God is ultimate and decisive, then this is the way you will learn to talk about the choices of the Christian life: I choose not to let sin reign in my body, because God is at work in me and will not let sin reign in my body (see Philippians 2:12-13; 3:12; 1 Corinthians 5:7).
Romans 6 puts everything into a different light and gives me hope and courage to give myself again as a slave to righteousness.