> The teachings of Jesus supersede the stuff from the Old testament (the one with all not very nice things) however they are rather vague and undefined.
Except Jesus said that he didn't come to abolish the law but to fulfill it, and not one stroke of a letter of the law will pass away. So he didn't change anything about slavery, mistreatment of women, etc.
He also said 'Love your neighbor as yourself' and a bunch of similar things. Which kind of makes it complicated. I guess selling other people to slavery is fine as long as you also sell yourself (just like mistreating others).
> didn't change anything about slavery, mistreatment of women, etc.
The "fulfill" bit is rather ambiguous. AFAIK the most popular interpretation (certainly when it comes to ceremonial rules like not eating pork/shellfish/etc.) is that his intention was to "bring the law to its intended goal/purpose" rather than to maintain it in perpetuity.
But none of that ever applied to gentiles. Not before Christ, not after. Jews today do not claim that non-Jews are obliged to, or even ought to, perform any Mitzvot whatsoever -- and that's despite generally acknowledging that there are universal moral laws which bind all "children of Noah".
So if the remaining Jews continue following the Old Covenant, but others choose to rather follow Jesus' 'New and Eternal Covenant', then where would this obligation towards Old Testament law come from?
To be fair modern Jews don't really follow the laws from the book of Deuteronomy (the one with rape -> marriage thing..) either due to other (but in a way kind of similar) reasons
Except Jesus said that he didn't come to abolish the law but to fulfill it, and not one stroke of a letter of the law will pass away. So he didn't change anything about slavery, mistreatment of women, etc.