Harry, Ron, Hermione, Neville, Ginny and Luna go to the Department of Mysteries. They find a prophecy that says "..and the Dark Lord will mark him as equal, but he will have power the Dark Lord knows not... and either must die at the hand of the other for neither can live while the other survives." Harry and his friends fight the Death Eaters and Sirius is killed by Bellatrix Lestrange. Dumbledore and Voldemort battle one another and Voldemort possesses Harry. Harry rejects Voldemort and says that he pities him because he'll never know love and friendship. Minister Fudge and other members of the Ministry of Magic see Voldemort (as he escapes quickly) and they finally know and realize that he's back. The Ministry of Magic admits that Voldemort is back and Dumbledore is re-instated as the Headmaster of Hogwarts. Dumbledore admits to Harry why he has been distant lately: he did it on purpose so that (maybe) Voldemort would be less tempted to get to Harry. Luna Lovegood puts up Wanted flyers at school for her belongings (they were stolen by students as a joke and not by nargles) and she finds her sneakers. Harry, Hermione and Ron leave Hogwarts until next year and Harry mentions that they have on their side something that Voldemort lacks: friendship, love and that those are things worth fighting for.
Syd
Answer: When Voldemort originally attacked Harry, he was acting on information provided to him by Snape. But Snape's information was not complete, ergo why Voldemort lost his powers. He wants the prophecy in order to hear it in its entirety, because he believes it will give him the information he needs to kill Harry.
Cubs Fan ★