What I love about this twist is how it changes the interpretation of so many other things that were said throughout the story. For example:

"Purposeless?" said Professor Quirrell. "Oh, but the madness of Dumbledore is not that he is purposeless, but that he has too many purposes.

It turns out PQ was right in that the madness of Dumbledore was not purposeless, however much his going around and "snipping all the threads of destiny" to constrain future events would, to anyone without all the knowledge of prophecy, look like many divergent purposes. Even Dumbledore himself didn't know how or why some of them fit into the whole picture. But it was all done in service of his one true goal. And if the service of that goal had involved killing Harry or framing Hermione? Well,

"Who knows what the Headmaster thinks he has reason to do, when he has found reason to do so many strange things already."