Had absolutely nothing to do with God condoning slavery. It was acknowledgement that slavery (an evil) existed.
Paul urged Christian slaves (in the passage you cited) to continue to obey their earthly (that is, human) masters, even though, by virtue of being Christians (a word I have little use for these days), they were no longer slaves in God's eyes, but free in Christ.
Moreover, Paul told those slaves not just to obey those earthly masters for the sake of avoiding punishment for disobedience, but to obey them sincerely and willingly, as if they were actually serving God, since it was God who had placed their masters in authority over them in this world.
It is part of the separating the wheat from the chaff. There will be MORE slave-masters in this country and they will be dealt with just as the slave-masters in Egypt were ... only this time will wrap it up.