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? To whom ye yield yourselves - Can you suppose that you should continue to be the servants of Christ if ye give way to sin? Is he not the master who exacts the service, and to whom the service is performed? Sin is the service of Satan; righteousness the service of Christ. If ye sin ye are the servants of Satan, and not the servants of God.
The word δουλος, which we translate servant, properly signifies slave; and a slave among the Greeks and Romans was considered as his master's property, and he might dispose of him as he pleased. Under a bad master, the lot of the slave was most oppressive and dreadful; his ease and comfort were never consulted; he was treated worse than a beast; and, in many cases, his life hung on the mere caprice of the master. This state is the state of every poor, miserable sinner; he is the slave of Satan, and his own evil lusts and appetites are his most cruel task-masters. The same word is applied to the servants of Christ, the more forcibly to show that they are their Master's property; and that, as he is infinitely good and benevolent, therefore his service must be perfect freedom. Indeed, he exacts no obedience from them which he does not turn to their eternal advantage; for this master has no self-interest to secure. See on Romans 1:1 (note).