the first two chapters of Prisoner of Azkaban are actually incredibly interesting if you reread them knowing the entire plot and the ending.
let's start with Wendelin the Weird.
it's essentially a fragment of the lore, a passage taken straight from a history textbook. on the one hand, yes, it's a direct piece of world-building.
on the other hand, what do we actually see? from the Muggles' point of view, it looked as though they were executing the guilty. but the point is that if it really was a witch, she wouldn't burn. the people who actually suffered were those who had no magical abilities at all.
so right from the beginning we get this theme of innocent people being punished, while those who are actually responsible walk away unscathed.
and, at the same time, the idea that reality is nothing like what it seems at first glance.
Aunt Marge breeds bulldogs. she breeds dogs. she raises these beasts that are openly hostile towards Harry, that pose a danger to him, that Harry is afraid of because she used to set them on him... just because she could.
much later, in Order of the Phoenix, Severus even asks about one of those dogs, but that's beside the point.
what's much more interesting is the way she talks about breeding. she argues that bad traits are inherited. that if the bitch is bad, then her litter will be just the same.
doesn't that remind you of another dog?
one who comes from a family with, let's say, highly questionable beliefs, values and preferences. one whose guilt everyone accepted because it wasn't difficult to believe.
after all, the apple doesn't fall far from the tree.
in the end, it's hard to say how much of Sirius's story was nature versus nurture, based on everything we know about him. and yet.
naturally, she also brings Harry's parents back into the narrative, something that didn't really happen in Chamber of Secrets. and, in effect, all of this ties into Harry's eventual reunion with his parents' friends.
and then there's the fact that this is the first and only time Harry runs away from home.
at roughly the same time, though a little earlier, someone else escapes from his own prison. someone who had also run away from home during his school years. and it is in this very book that the two of them are reunited.
after running away, Harry thinks that, at this point, it doesn't really matter anymore. he's already broken the law, he's almost certainly become a criminal, and now he'll have to stay on the run, live like a homeless person, and never return to Hogwarts.
which is, incidentally, exactly what the other fugitive is doing.