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? But thanks be to God, that you who were once slaves of sin have become obedient from the heart to the standard of teaching to which you were committed, and, having been set free from sin, have become slaves of righteousness. (Romans 6:16-18 ESV)
Either: you have a choice. You can either obey sin or you can obey righteousness. No longer must you show up to the taskmaster of your own flesh and say “yes.” You can say, “no.” Why does Paul saturate this description with slave language? A slave among the Romans was considered his master’s property, and he could do with him as he wanted. Under a bad master, the slave lived a dreadful life. His ease and comfort were of no concern; he was treated worse than an animal; and, in many cases, his life hung on the mere whim of the master.
That’s what the old slave master, sin, does. Satan cares nothing for you. And when you come to Christ, his hatred for you intensifies. Your old nature, the sinful nature that you possessed when you came to Christ, you still have. Deep within you is the desire to sin. When you give in to that old sin nature, you are throwing away the freedom given you in Christ. Your own evil lusts and appetites become your most cruel taskmasters.
The truth is that you choose your master—and you do not have to show up at your master’s house one more day. You can be free. As a Christ-follower, slavery to sin is voluntary. Look at what Paul says. You are a slave either of sin resulting in death, or of obedience resulting in righteousness.
Why use the same term, slave, to refer to believers? It more forcibly shows that we are our Master’s property; and that, as he is infinitely good his service must be perfect freedom. Jesus Christ asks no obedience from us that he does not turn to our eternal advantage because He has no self-interest to secure. You see, before Christ, you had no choice. The temptation came along, you gave in, and you fell to it. Now you have a choice. You have God, in the form of the Holy Spirit, living inside you. When temptation comes, you don’t have to say yes.