What does Romans 6:19 mean?
In the previous verse, Paul wrote that Christians have been set free from sin, and have become "slaves" of righteousness. Now he seems to suggest the concept of slavery is not a perfect description of our allegiance, in Christ, to God's righteousness as our new "master." He writes that he uses this "human term" because of the limitation in our ability to fully understand what it means to be under the authority of righteousness."Slavery" is a charged term in modern society, but it carried a very different meaning in the ancient world. The "chattel slavery" which treats human beings as animals or literal property was not the norm, in that era. Still, there were some who were enslaved in that kind of bondage, so perhaps Paul wants to be sure none of his readers picture our relationship with God in terms of a fearful or degrading experience. Rather, he acknowledges that his metaphor is not exactly a perfect fit, though he will continue to use it.
As he refines the idea, Paul will make clear that Christians are absolutely under the full authority of God to be used for His purposes. However, God remains a loving Father and does not compel us to act against our will. He is always Master, and He is ever calling believers to obey Him.
Paul makes it clear that God wants us to choose obedience to Him. Why else would we need to be told to do so? He commands those in Christ to present their members—bodies, minds, will, etc.—as slaves in the service of righteousness. He tells us to do this in the same way that we once presented ourselves as slaves to impurity and lawlessness.
Paul describes those who are not in Christ as under compulsion to serve sin. They must obey their sinful desires. That is their work. The result of that work? More and more lawlessness. That is, they succeed in creating more sin in their lives and in the world.
Those in Christ, on the other hand, are used by God to serve righteousness. What comes from that, Paul writes, is sanctification or holiness. The New Testament often uses the word "sanctification" to describe the process of being made holy, of becoming like Christ. God uses our service to righteousness to contribute to that process.