Know ye not, that to whom ye yield yourselves servants to obey, his servants ye are to whom ye obey; whether of sin unto death, or of obedience unto righteousness? But God be thanked, that ye were the servants of sin, but ye have obeyed from the heart that form of doctrine which was delivered you. Being then made free from sin, ye became the servants of righteousness. (Rom 6:16-18)
The word ["servants"] in Romans refers to one who is bound to another, a slave. There are two words in Greek referring to a person in slavery. One speaks of a slave taken in war. The other refers to a person born into slavery. The latter is the one used in Romans. (Wuest, Word Studies from the Greek New Testament)
Kenneth Wuest's comment gives rise to some special thoughts about our choice to obey Christ. There are certain aspects of our enslavements that bear special scrutiny.
In the passage quoted above we are described as servants (bondslaves) to either sin or righteousness. We were born into this slavery, first to sin and then to obedience. That is not to say that we were born sinful. A child born to a slave family was destined to be a slave. The enslavement did not start at birth, though, but several years after, when the child was old enough to perform the duties of a slave. Just so, we were born in slavery, but did not perform the duties of a slave until we were able to understand sin. But we are also born into slavery to obedience and righteousness. A person born into slavery had a special relationship with the master, because he was raised in that household. If that same person was sold to a new master, he was still born a slave but did not have the same relationship to the new master. That is not how it is when we change from slaves of sin to slaves of righteousness. We are born into the new form of slavery. It is more than just a change of masters. It is a new birth into a new slavery. The picture Paul gives in the context of Romans 6 emphasizes this. In becoming slaves to righteousness we don't just change masters. We change births. We change lives. "Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life." (Rom 6:6) When we are born into slavery to Christ we are no longer the same person we were when we were slaves to sin.
Paul says that we may be slaves, but in either case we are unusual slaves. We are born into slavery, but we have a choice. Granted, any slave has a choice. Usually the choice is to obey the master or be punished; ultimately, obey or die. Paul says we have a choice to yield to sin. But in that case it is a choice to obey and die. We also have the choice to disobey, but then we disobey and live. If we choose to disobey sin, we choose to be born into a different slavery. This new slavery has choices, too. But in this new relationship the choice is obey and live. What a difference!
We have no choice but to be slaves. We do have a choice as to the master and the wages. Whose slave are you?