I always liked the message that doing a thoughtful good deed can turn into other good deeds. The family next door thinks Sara is a beggar and the son gives her a pence, or whatever it was... while it's a kind gesture, it does not actually help Sara. But when Sara, starving herself and having found money on the ground, buys 6 rolls and sees someone who is even hungrier than she is and gives the child all but one. The baker sees this and, knowing that Sara herself could have scarfed them all down, decides to give the beggar child more and eventually invites the child to live with her and work in her shop, and has been giving hungry children bread as often as she can because of Sara's deed.

And then once Sara is rich as fuck she tells the baker to give hungry children bread whenever and she'll pay for it.

And likewise, a bad deed will bite you on the ass. Miss Minchin is cruel to Sara and, when Sara's fortune reverses, she does not get kindness in return. If she had shown Sara kindness, despite her new station, then she may have benefited from Sara's newfound wealth. Not just financially but with her reputation, which I imagine would be shattered once the news got out of what she had done.