Romans 6:19

I speak after the manner of men because of the infirmity, of your flesh: for as ye presented your members as servants to uncleanness and to iniquity unto iniquity, even so now present your members as servants to righteousness unto sanctification.

Paul continued in these words to plead for personal righteousness on the part of every person who had named the name of Christ, the last clause of this passage being a commandment for the disciple to proceed toward that personal holiness without which no man shall see the Lord (Hebrews 12:14). This personal holiness is what is usually meant by sanctification. The basis upon which Paul dared to lay down such an assignment had just been explained. It was the legal justification of the believer which took place upon his baptism into Christ. Paul was a little apologetic here for introducing such an illustration as that of manumission of a slave, but he justified it on the basis that the weakness of people required such a dramatic and familiar comparison. Just as it was unthinkable that a manumitted slave would keep on working for his old master, so it is unthinkable that a Christian would go on serving Satan after being delivered from the bondage of sin through his faith and obedience of the gospel.

To paraphrase this verse, without metaphor, Paul was simply telling the disciples that just as they once used all their time and resources in committing impure and lawless deeds, now they should use all their energies in doing the things that honor God and bless humanity. "Iniquity unto iniquity ..." means more and more iniquity.

Servant ... as used in this chapter actually means "bondservant" or "slave," but the translators have wisely softened the impact of it, due to the repugnance of the term "slave." Yet it should never be forgotten that Christians are indeed "slaves" of Christ in the absolute sense of the word, having been purchased by him when they were sold unto death under sin; he redeemed them, and they owe him absolute and total obedience; they may not demur at anything Christ commands.