The First Prophecy: More Than Meets the Eye?
An original editorial by Alice Willford
...And so, since his return to his body, and particularly since your extraordinary escape from him last year, he has been determined to hear that Prophecy in its entirety. This is the weapon he has been seeking so assiduously since his return: the knowledge of how to destroy you.
Dumbledore, OotP page 740 (British edition)
A moment I'm sure we all remember very vividly. A moment of terrible suspense, in which the universal unasked question is: what on earth does the prophecy say?
Good question. Is it just me, or is something huge missing here? From the above quote, we are led to believe that the prophecy will tell us (and Harry) how Voldemort can kill him. However, we are not told this at all. In fact, analyzing it now, it appears to me that if Voldemort had heard the prophecy, he would have gained very little new knowledge.
To clarify this, we know that Voldemort was already aware of the fact that both Harry and Neville were potentially a danger to him. We can further assume that, after Voldemort's disastrous attack on Harry, he ruled out Neville as a threat. It is therefore safe to deduce that he already knows Harry is The One.
What he doesn't know is that during the attack on Harry he accidentally "marked him as his equal." However, even if he did know this, what difference would it make? It is too late for Voldemort to do anything about it now. He already knows that Harry has unusual powers--the ability to invade Voldemort's own mind, for one--and it is no longer a secret that Harry can speak Parseltongue. Voldemort has probably realized that, to quote Moody, "there's something funny about the Potter kid."
He also doesn't know that "either must die at the hand of the other," but once again, what difference would it make if he did? Voldemort would have continued in his attempts to kill Harry whether he knew the contents of the prophecy or not, and he would assume that Harry, as "the one with the power to vanquish the Dark Lord," could potentially have the power to kill him.
We can see from this that, apparently, the prophecy would have given Voldemort little new information and doesn't reveal how to kill Harry. Why then was it so imperative to keep him from hearing it? Why did people like Arthur Weasley repeatedly risk their lives in an attempt to guard it?
One theory is that there is something in the prophecy that we and Harry have completely missed and that will become clear in later books. It is safe to assume, if this is the case, that Dumbledore knows what it is but is not telling, perhaps because he doesn't want to give Harry any further unnecessary burdens; or maybe because it will ruin the "wonderful plan" that he speaks of, or...well, there could be a hundred reasons.
Another theory is this: the reason we haven't spotted this information that Voldemort wants so badly is that Dumbledore purposefully kept a part of the prophecy back. We have never been told how the Pensieve works, so we cannot be sure that the memory Harry saw was a complete one. Dumbledore can control the Pensieve as he sees fit, can show Harry what he wants to show him, and he may even be able to alter memories to suit his convenience--they are his to control, after all. Why he would do this I once again cannot answer; but if it is the case, I believe it will become highly significant in later books.
A final theory I have is that Dumbledore is deliberately leading Harry off the scent. If taken at face value, the contents of the prophecy are highly significant to Harry, and a revelation to us, but not very useful for Voldemort. Nowhere is it stated that it was actually the prophecy that the Order was guarding. We only know that they were standing guard over the door to the Department of Mysteries. Indeed, at the beginning of OotP, Sirius describes whatever it is as a "weapon," which seems an odd way to talk about a small, spun-glass prophecy. My theory is that, rather than guarding the prophecy itself, the members of the Order of the Phoenix were in fact guarding something else which it was imperative that neither Voldemort nor Harry discovered. The contents of the locked room, containing "a power at once greater and more terrible than death" perhaps?
Much as I would like to believe this last theory, I realize it has some gaping holes. If it were true, the Order could simply have told Harry to hand over the prophecy when they arrived to the rescue at the end of OotP, which would have made it far easier for them all to escape unharmed. But I believe the first two theories are definitely possible. Indeed, I think that one of them must be true because, as I have said, the prophecy (at least as related by Dumbledore) would have given Voldemort little useful information. This raises interesting questions, not only about the explanation given by Dumbledore in "The Lost Prophecy," but also about the nature of the Pensieve, what it does and how it works.