Slavery was a practice commonly used and accepted in the ancient and especially Roman world. Christianity, by nature, directed at doing good things to the other people, had different attitude. Saint Augustine also had his opinion.
Early Christianity showed some signs of goodness toward slaves. A slave marriage was recognized, the slave’s release was considered an act of goodness, and on their tombstones there was not mentioned information about status.
On the other hand, the growth of the Church’s institution has led to the evolution of the approach. Often, the Church condemned the escape of a slave from master and denied them Eucharistic communion.
Saint Augustine himself (354-430 CE) in his work De civitate Dei asserts that slavery is the result of sin, which linked people by dependence, and which does not come from nature, because it was not God’s will. At the same time, Augustine admonishes slaves to obey their masters and to serve them faithfully, so that if they can not be freed, though they can make their slavery to some point freed. This can be done by showing a great loyalty and love until the slavery ends.
Saint Augustine also argued that Christian emperors could not erase the trace of the sin of humanity, because it would require exposure to social order and hence slavery could not disappear.