Respecting your masters is not the same as endorsing slavery but whatever. Ancient traditions aren't what are being endorsed by Christianity. Last I checked I don't have to marry my brother's wife should he perish.
Lots of teachings in the NT have that context... For example:
Where JESUS says, "If someone strikes you in the right cheek, offer him your left cheek" The passage isn't endorsing subjugation by beatings, in fact it acknowledges the fact that the beating might be unjust in nature - nevertheless, the point JESUS was trying to convey was temperance and restraint - and at a more powerful level forgiveness.