Romans 6:16 - Do you not know that if you present yourselves to anyone as obedient slaves, you are slaves of the one whom you obey, either of sin, which leads to death, or of obedience, which leads to righteousness. Paul says that everyone is a slave and lays out two possibilities: 1. We are slaves to sin which leads to death. 2. We are slaves to obedience which leads to righteousness. Paul's language here, especially in (2) above is a little difficult. When Paul says that we are slaves he could either mean this in an existential sense or in a judicial sense. If we are slaves existentially, it means that we must sin. We are existentially ruled by the flesh. But if we are slaves judicially, it means that we owe a debt because of sin - namely death. We are slaves in the sense that we are bound to pay a debt. I think Paul is talking about the existential kind of slavery here. We obey either the flesh or the Spirit. "Slaves to obedience" I think is another way of saying that we are slaves of God's law. Now to what this slavery leads to. A life devoted to the flesh leads to death. But a life devoted to the law leads to righteousness. What does it mean that "obedience leads to righteousness". Again, righteousness could be understood in existential or judicial terms. If existential, Paul would be saying that a life devoted to the law leads to an existential righteousness. But if judicial, Paul would be saying that a life devoted to the law leads to a legal declaration of righteousness - i.e. justification. I think what Paul is saying in (2) is that obedience leads to justification. This is interesting because it shows how flexible Paul's language can be when referring to justification. When he says "righteousness" here, he is talking about God's judgment that a person is righteous. He is saying something very similar to what he says in Romans 2:13 that "the doers of the law will be justified." Of course this does not mean that we can be justified by our obedience to the law. Paul has already established that while this is possible in theory, it is impossible for sinners like us. We need to be justified by another way. So Paul's "obedience which leads to righteousness" is hypothetical here. Yet I think it's interesting to note how Paul can use the word "righteous" and "justification" synonymously. Indeed they are even more closely related in Greek than in English.