The Word in Life Study Bible, New Testament Edition, (Thomas Nelson Publishers, Nashville; 1993), p. 546
Paul uses a powerful image when he pictures one's relationship either to sin or to obedience as slavery (Rom. 6:16>). The Roman Empire was heavily dependent on slaves to take care of its hard labor and menial tasks. In fact, many of Paul's Roman recipients may have been slaves, since perhaps half the population or more were under servitude by one historian's estimate.
Slaves were taken from the many nations that Rome conquered. Those assigned to the empire's widespread construction projects or to its mines had a hard lot. Fed a subsistence diet, they were worked to exhaustion. Injuries and disease were common, and once they were too sick to work, or in rare cases too old, they were abandoned.
Household slaves, however, enjoyed better conditions. Nearly every Roman home owned at least two or three servants, and some had hundreds. They assisted the women in maintaining their homes and raising their children. Slaves with occupational expertise proved particularly valuable in the workplace, and some businesses were entirely dependent on these imported, cheap laborers.
Slavery existed long before the Romans, of course. The Bible records several different forms of slavery in ancient times: domestic slavery, as illustrated by Hagar (Gen. 16:1>); state slavery, as illustrated by the Israelites under Egypt (Ex. 5:6-19>; 13:3>); and temple slavery, as illustrated by the slaves of the Levites for temple service (Num. 31:25-47>; Josh. 9:21-17>).
Curiously, the Bible does not directly condemn slavery as an institution, though it contains warnings about the practice of slavery (Amos 1:6-9>; Rev. 18:13>). The Old Testament Law did regulate Israel's treatment of slaves (Ex. 21>; Deut. 15>). Repeatedly, the people were instructed not to rule over a fellow Israelite harshly (Lev. 25:39>; Deut. 15:14>). If a master beat a slave or harmed him, the law provided that the slave could go free (Ex. 21:26-27>); and the killing of a slave called for a penalty (Ex. 21:20>).
In the New Testament, slaves were advised to obey their masters (Eph. 6:5>; Col. 3:22>; Titus 2:9>). Paul appealed to Philemon to receive back Onesimus, a runaway slave who became a Christian and therefore a brother (see the Introduction to Philemon). This was an illustration that in Christ, social distinctions such as slavery no longer apply (Ga. 3:28>; Col. 3:11>). Elsewhere Paul counseled believing slaves to seek freedom if they could (1 Cor. 7:21>).
Under Jewish law, no Hebrew was to be the permanent slave of another Hebrew (Ex. 21:2>; Lev. 25:37-43>; Deut. 15:12>). If a slave desired to continue with his master, he would have a mark made in the ear to signify that he had chosen to remain a slave (Ex. 21:5-6>). A slave could also buy his freedom, or another person could buy his freedom for him (Lev. 25:47-49>).
Among the Romans, an owner could free a slave outright, or the slave could purchase his freedom by paying his owner. Freedom could also be arranged if ownership was transferred to a god. The slave could then receive his freedom in return for contracting his services. He would continue with his master, but now as a free man.
Perhaps Paul had that sort of arrangement in mind when he described the moral choice of which master one would obey&md;sin or righteousness (Rom. 6:16>). For as believers, we have been freed from sin, and in fact are now owned by God. We are now free to serve God. Yet we still have a choice to serve either sin or God. In light of the realities of slavery, it's worth considering: Which master are you serving? Which one is likely to treat you better?