Paul now considers the third great relationship in society, that between masters and slaves, or its equivalent for most of us, employers and employees. If the slave is to render conscientious service to his master, how much more the free man? In New Testament days slavery was prevalent in society and in the Roman world this was a far less well regulated and humane form of slavery than that prescribed by the law of Moses.
Many find this instruction surprising. The original Greek has owned slaves in mind. Was Paul in favour? See Leviticus 25, Deuteronomy 15 and 24. Anyone who stole an Israelite was to die (Exodus 21:16). Slavery was kept under Moses only because there were some who lost all and were impoverished, and to pay their debts they went into bondage (Leviticus 25:39)., but if you had such a slave, you have to treat them just like a hired servant (Leviticus 25:40). The only difference was that they received no wage, but otherwise they were entitled to the same time off, and so on. Also the time to serve was six years, then slaves must be released (Exodus 21:2). When he went free, he must be given liberally from the produce of the land (Deuteronomy 15:14); you had to set him up in life. The aim was to remove slavery. But Paul spoke to men living in an unreformed age. Though Scripture is against slavery and it would go in future, yet Paul speaks to those living in circumstances beyond their control. The gospel can flourish in every situation.