Therefore do not let sin reign in your mortal body, that you should obey it in its lusts. And do not present your members as instruments of unrighteousness to sin, but present yourselves to God as being alive from the dead, and your members as instruments of righteousness to God. For sin shall not have dominion over you, for you are not under law but under grace.
History and Context:
As noted before the book of Romans was written by Paul to the church in Rome, probably around 55 - 57 AD. The history and beginnings of the church in Rome is not fully known. Most scholars believe that they established themselves without the help of any Apostle and without seeing any signs or miracles. There was a strong mix of Jewish and Gentile Christians in Rome at this time and they seem to have gotten in many arguments. The Jewish Christians wanted the Gentiles to be circumcised and to follow the law to the letter, whereas the Gentile Christians attempted to say that they were better and that the Jews were rejected as God's people. Paul addresses both of these issues in his letter.
Since Paul is writing to two different groups of people, with two opposing viewpoints which are both wrong, Paul ends up almost in a discussion with himself. He spends a few chapters discussing law and grace, and how they relate with each other. Here Paul is talking about the power that sin has, or had, over us. He says earlier taht we died and raised with Christ and that for this reason sin no longer has dominion over us. If we died then we died to sin, if we were raised then we were resurrected in His power and grace. His grace then allows us to be freed from sin. It is the grace of God that not only cleanses us from our sin, but also frees us from it's power over us. Paul presents the question, How could we who have been freed from sin return to it?
Understand your freedom, understand grace! You don't have to sin. You are free from it. Don't listen to the enemy. The enemy wants you to think that you are a fallen human and can therefore not help but sin. You have been freed from your fallen nature and can choose not to sin. Buit also understand that if you do sin, run straight back to God! Don't spend time worrying about whether He would accept you. Know that He will. That's what His grace and mercy are there for. To cleanse you and give you power to not do it again!
Lord, I don't want to sin again. Help me to understand the power that you have given me in your grace. Help me to understand your desire to free me from sin's dominion. I love you Lord! In Jesus' name, Amen!