New Testament writers addressed the context of their culture. Slavery was an way of life in that day and age. Many people found themselves to be slaveholders through inheritance or property exchange. Then they became Christians. Many slaves had nowhere to go and no means of support if they were set free. In some cases it would have been evil to set your slaves free just to be rid of the expense of feeding them. The Bible teaches us to apply Christ's principles of selfless love no matter what situation we find ourselves in.