Ephes. 6:5-9 (ESV)
Slaves, obey your earthly masters with fear and trembling, with a sincere heart, as you would Christ,  not by the way of eye-service, as people-pleasers, but as servants of Christ, doing the will of God from the heart,  rendering service with a good will as to the Lord and not to man,  knowing that whatever good anyone does, this he will receive back from the Lord, whether he is a slave or free.  Masters, do the same to them, and stop your threatening, knowing that he who is both their Master and yours is in heaven, and that there is no partiality with him.
Slavery was a reality in Paul’s day. It is even today in some parts of the world. The Bible doesn’t forbid it, neither does it command it. For me, I am glad that slavery has been abolished in Christian countries. Though I think one would have to be blind to not see that abolishing slavery has not quite led to Shangri-La. Sweatshops and exploitation of the poor are still problems. Race relations aren’t always what they could be.
Perhaps we don’t find much helpful for us here in this admonition to slaves and slave owners. But I think there is good advice here that employees and employers can take to heart. Render your service with a good will as to the Lord; acting out of a sincere heart is good advice. In fact what the Christian does in his vocation he does do to the glory of God, and as a service for God. We serve God by serving our neighbors, and our bosses, by serving others. And employers do well to remember to treat their employees as humans it goes along way in garnering productivity.