Testing an idea: Why did righteous Sarah mistreat Hagar? Seems out of character right? Could it be because (a) she wanted to have Abraham's son via Hagar; and (b) that only works if Hagar has the status of a slave; and as the verse tells us (c) Hagar, with Abraham's blessing and support, had ceased to behave as one.
Perhaps Sarah mistreated Hagar only for the purpose of re-asserting herself as Hagar's mistress which she considered crucial if the son Hagar was carrying was to truly be considered Sarah's son.
Of course, all of this rests on the premise that Sarah was, in fact, righteous. Perhaps she wasn't. Or, perhaps she was, mostly, but the mistreatment of Hagar happened on an off-day. Awesome people have bad days, too, don't they? And if you want to get right down to it, don't ask how could righteous Sarah beat on her slave. Ask how could righteous Sarah assert ownership of another human being in the first place.So, let me ask the question this way. Our midrashim depict Sarah as a prophet. The law codes say you can't become a prophet without having a sterling character. Perhaps for that time in place, raging at your slave out of jealousy was not incompatible with having a sterling character. But in our time the two are mutually exclusive. So (here comes the question) how do we reconcile (a) our understanding of what it means to be a good person with (b) the verse about Sarah going psycho and (c) the interpretations that say she was a prophet, and therefore righteous.
I know, I know. We're now into midrashim on midrashim but this is what passes for learning nowadays.