Paul makes an interesting statement in chapter 6 of his letter to the Romans: “Don’t you know that if you offer yourselves as obedient slaves, you are slaves to the one you obey: slaves of sin leading to death, or slaves of obedience leading to righteousness?” Involuntary servitude, in which people are bought and sold and forced to perform the will of their owners, still exists to an appalling extent in the world today. But here Paul is talking about voluntary servitude.
The problem is that there is a fine line between freedom and slavery. Freedom to eat anything becomes slavery to overeating. The freedom offered by a credit card becomes slavery to debt. The freedom offered by recreational drugs becomes slavery to addiction. The freedom offered by a high-paying job becomes slavery to long hours in the office. The freedom offered by a relationship becomes slavery to keeping the other person happy.
According to Paul, you can choose what you want to be a slave to. You can be a slave to sin – that is, to anything which feeds your selfish desires or which does not serve any ultimate good purpose – and that path leads in the end to death. Or you can choose to be a slave to obedience – that is, to putting the interests of others before your own, and doing things which serve a good ultimate purpose – and that path leads to righteousness.