In Ephesians 6:5-9, Paul speaks to Christian masters and slaves. We often assume that slavery in the New Testament is equivalent to the race-based slavery of African slave trade.
But slavery in Paul’s day was not like our nation’s race-based slavery, rather it was more similar to indentured servitude. Paul was instructing the slave owners on how they were to manage their workers. He reminds them that they will, one day, answer to the Lord for how they treated their employees. The slaves were encouraged to find purpose and satisfaction in their work, and to work as unto the Lord. Some of the slavery in the ancient world was brutal and harsh. But there was also evidence that many slaves lived normal lives and were paid a competitive wage. They were required to remain with their employer for an average of ten years. These slaves were often prisoners of war, those who were in debt [note there was no bankruptcy in those days], or serving time for a crime. Some slaves were well educated and held degrees. Some were doctors, professors, administrators and civil servants. The ancient world could not conceive of a society without indentured labor. No one, not even slaves, conceived of a world without slavery because it was so ingrained in their ancient culture. Paul didn’t seek to abolish slavery but to transform it from the inside. This is what we are seeing in passages like Ephesians 6:5-9. “What [Paul’s letters] do is to bring us into an atmosphere in which the institution of slavery could only wilt and die.” — F.F. Bruce, Paul: Apostle of the Heart Set Free Christianity brought about the idea that slavery was an abominable institution and needed to be abolished. But that would be done by changing the hearts of those involved. Finally, Paul speaks of how Christ became a slave for us and how we are to become a slave for Him. "In your relationships with one another, have the same mindset as Christ Jesus: Who, being in very nature God, did not consider equality with God something to be used to his own advantage; rather, he made himself nothing by taking the very nature of a servant, being made in human likeness. And being found in appearance as a man, he humbled himself by becoming obedient to death— even death on a cross!" — Philippians 2:5–8 Slave owners were to see their slaves as brothers in Christ [1 Corinthians 7:22-23]. Paul tells us in Galatians that we are all equal in Christ; there is neither slave nor free. Many critics simply assume that the Bible endorsed slavery. In reality, the Gospel destroyed the heart of slavery. Paul is not denouncing the institution of slavery, but he is speaking to Christians within the institution about how they are to conduct themselves. And that was revolutionary.