Not just our understanding, the teachings and scripture seem pretty clear. They could be summed up as follows:
About 3 or 4,000 years ago, slavery was completely acceptable. A slave could be treated as inheritable property and the rules about violence and beatings (even to death) were different to those applied to free men.
Around the time of Christ, things become more subtle. Slavery is still morally acceptable and commonplace but the way they are treated is less harsh.
In the present, slavery is considered morally reprehensible and unacceptable.
What was once explicitly acceptable and moral according to Scripture would now be classed as wholly unacceptable.
re read post 145 (I know long) but the answer is there
:)