Romans 6:15-18 (NIV)
15 What then? Shall we sin because we are not under law but under grace? By no means!
16 Don't you know that when you offer yourselves to someone to obey him as slaves, you are slaves to the one whom you obey--whether you are slaves to sin, which leads to death, or to obedience, which leads to righteousness?
17 But thanks be to God that, though you used to be slaves to sin, you wholeheartedly obeyed the form of teaching to which you were entrusted.
18 You have been set free from sin and have become slaves to righteousness.

In verse 14 Paul reminds them that they are under grace and not under the law. Paul knows that this truth can then be used to justify sin and so he takes this head on. We are out from underneath the burden of having to fulfill the law in order to gain access to God and heaven. For this truth of freedom in Christ we should rejoice, but we must understand that Christ has standards for us to live by. If we fail to live up to these standards this does not mean we are tossed aside. God's grace will bring us back and show us forgiveness in Christ. The language that Paul uses is very strong in order to help followers of Christ to be enlightened on this subject of sin. If we obey sin then we are slaves to sin. Paul then says, "You have been set free from sin and have become slaves to righteousness." Are you a slave to righteousness? We are free when we are a slave to God and his righteousness. One time I was sharing with a friend who did not go to church and he said to me, "I want God and Satan to leave me alone and let me live my life as I see fit."

It seems to me this friend of mine sums up the spirit of the age which is: "I only want to serve me and everyone else leave me alone". It is counter intuitive thinking to propose that true freedom comes by way of being a slave to righteousness.

Freedom does not mean I am able to do whatever I want to do. That’s the worst kind of bondage. Freedom means I have been set free to become all that God wants me to be, to achieve all that God wants me to achieve, to enjoy all that God wants me to enjoy.

Warren W. Wiersbe