Continuity mistake: There are two scenes during which Harry is shown having visions of the Dept of Mysteries while he is asleep. The first scene occurs after Harry's confrontation with Seamus in the Gryffindor common room. There are shots of Harry lying in bed wearing a short sleeve, crew neck tee shirt, but when he is startled awake by the vision of Voldemort, he sits up wearing a buttoned henley tee. The next day is the first day of Defence Against the Dark Arts class with Umbridge. That last shot of Harry in the henley tee shirt was cut from a later scene. Later in the film, when Harry has the vision of Arthur Weasley's attack, he is wearing the henley tee shirt. (00:34:00 - 01:09:35)
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 ★