It's also confirmed that "Dumbledore's reasons for not giving Snape the Defense Against the Dark Arts job will be revealed." in the next bk.
here's another theory, i found it somewhere...
Prophecies in Harry Potter
One of the oddest unexplained elements of the Harry Potter books are Professor Trelawney's two "real" prophecies, both having to do with Harry Potter. It appears that she is merely a vessel for some greater being to pass along valuable information in the form of a prohecy. In fact, this doesn't seem all that uncommon in the wizarding world considering all of the prophecies sitting in the Deparment of Mysteries in Harry Potter and the Order of the Phoenix.
Can a prophecy become a tool of deception?
Should we question the validity of Harry Potter's prophecy - or any prophecy for that matter - because we do not know who is sharing the supposed 'wisdom'? Is it possible that a powerful witch or wizard, or perhaps some other being, could manipulate another creature in order to pass along a false prophecy? The Matrix Reloaded popularized the idea that an "Oracle" (not unlike a being speaking through Trelawney) might just be another means of control, that lies are possible. It is, of course, a question in the Harry Potter books that will fundamentally affect the events in book 6 and book 7. What do you think?
Applications of Time, Destiny, and Fate
Should the prophecy be questioned, or regarded as legitimate canon? Is there reason to believe that some powerful being, including possibly Dumbledore, exists to spread false and/or baseless prophecies simply to shape the world events? At what point does the TimeTurner affect the true nature of Fate in the Harry Potter books? Can Voldemort use one?
It's the last sentence that hit me the most... why doesn't Voldemort use a time-turner?