Joshua copied the same law onto a different set of stones to be read to a people that never knew slavery. Again the law was applicable to them.
We, facing many different situations, having many different backgrounds, at this time in history, are living by the same law.
God’s ways, His laws, the gospel transcends all time, all situations. It is just as vital to us as it was to them and it’ll be just as meaningful to the generations to come as it is now.