What does "while" mean in this context?

Question

“Well, Voldemort’s going to try other ways of coming back, isn’t he? I mean, he hasn’t gone, has he?”
“No, Harry, he has not. He is still out there somewhere, perhaps looking for another body to share… not being truly alive, he cannot be killed. He left Quirrell to die; he shows just as little mercy to his followers as his enemies. Nevertheless, Harry, while you may only have delayed his return to power, it will merely take someone else who is prepared to fight what seems a losing battle next time — and if he is delayed again, and again, why, he may never return to power.”
(Harry Potter and the Sorcerer's Stone)

Which of the meanings reported by the OALD is the one while has in the sentence?

• Used to contrast two things
• Although; despite the fact that…

Does it indicate the fact before mentioned or to infinitive clause followed?

Answer 1

I concur with la piquante's answer to your first question.

His answer to your second is semantically correct, but grammatically inaccurate: the it here is a 'dummy' employed in a cleft construction.

However, the sentence is very complicated. Note, first, that there are two distinct propositions here:

A. If Voldemort is delayed again and again ... (then) he may never return to power.
B. To delay Voldemort will merely take someone prepared to fight what appears to be a losing battle next time.

Let's simplify those radically, so the syntax becomes clearer:

1. If [ DELAY^1...n ] then [ DEFEAT ]
2. [ DELAY^{next time} ] will merely take [ HERO ]

1. Dumbledore's sentence is built on Proposition B, recast as an it-cleft:

   It will merely take [ HERO ] to [ DELAY^{next time} ]

2. At this point a common English construction we might call ONLY... AND comes into play. This construction is syntactically very similar to the IF ... THEN construction, and bears a similar interpretation: ONLY do this, AND that will happen. The ONLY element which introduces the condition clause may be any adverb or adverbial with the approximate sense of only—merely, just, but—and the consequence clause is introduced by and. These constructions are often used to motivate or warn:

   Only try, and I'm sure you'll succeed!
   Just mess with Big John and you'll see what happens.
   But screw your courage to the sticking-point and we'll not fail. -Macbeth

   This construction marries very readily with verbs like require/need/take:

   It only took one whistleblower, and the whole scheme collapsed.

   Dumbledore does just this. He moves the next time into the condition clause, where merely acts as the ONLY element, and combines the AND clause with the Proposition A conditional:()

   It will merely take [ HERO^{next time} ] and if [ DELAY¹ and DELAY² ...] (then) [ DEFEAT ].

Answer 2

1. 'While' here means although (4 on the OALD). If you replace while with although in this sentence, it makes perfect sense. The sentence is not really comparing two things: the fact that Harry has delayed Voldemort's rise to power is not in contrast to the fact that someone else brave enough to fight Voldemort could do that again, they're both working towards the same goal (defeating Voldemort.)

2. 'It' refers to what will keep Voldemort at bay here (that is, someone else fighting him again).