Romans 6:18

The slavery of the readers to righteousness was therefore voluntary. It seems that because of his very nature man must be the slave of something. "Righteousness" here is the result of following Christian teaching, and it is the equivalent of godly living. It is righteous character and conduct.

Paul did not say that every believer takes advantage of his or her freedom from sin’s tyranny to become a slave of God. He said his readers had done so, and in this he rejoiced. Dedication to God is voluntary, not automatic for the Christian (cf. Romans 6:13; Romans 12:1). If a believer does not truly dedicate himself or herself to God, he or she will continue to practice sin to a greater extent than he will if he does present himself to God (Romans 6:16).