Slavery as practiced in the ancient world was not the same institution as the chattel slavery in the European colonies, which is an entirely different moral gray area. It was more akin to our modern employment relationships if anything. And the following sounds like a reasonable expression of Christian morality, does it not?:

> 22 Employees, in all things obey those who are your employers on earth [lit. according to the flesh], not with external service [lit. eyeservice], as those who merely please men, but with sincerity of heart, fearing the Lord.

https://en.wikipedia.org/wiki/Slavery_in_antiquity