| Quote #1
He turned to smile at the tabby, but it had gone. Instead he was smiling at a rather severe-looking woman who was wearing square glasses exactly the shape of the markings the cat had had around its eyes. (1.47)
Rowling doesn't waste any time – we're only partway through chapter one and we've already witnessed our first Transfiguration. Here McGonagall transforms from a tabby cat into her real form – professor at Hogwarts. From context given later in the book, we know how hard just transforming a match into a needle is: given the ease with which McGonagall goes from cat to person, she must be a very powerful witch indeed.
| Quote #2
"I'm a what?" gasped Harry.
For Harry – and, we might imagine, anyone who's grown up only knowing about Muggles – learning that there's not only magic and wizards, but that he himself is one, comes as a pretty big shock. It's not just finding out that supernatural elements exist, it's discovering that he's one of those supernatural elements himself.
| Quote #3
"Wizards have banks?"
We're not sure what's more of a shock here: 1) the idea that "wizards have banks," just like non-wizards do, and that they would still value currency the way non-wizards do; or 2) that there are "goblins" in this world, and that they work at the wizard bank. For Hagrid, of course, who's grown up in this magical realm, it's just a matter of course. And really, for Harry, it shouldn't be too much of a stretch to start believing in goblins, when he's already been convinced about wizards.