The construction BE to VERB means, depending on context, BE expected/supposed/required to VERB. VERB may be any infinitive: simple, passive, perfect, or progressive (or any combination of these).
You are to leave immediately. = You are required to leave.
The prisoners were to be executed at dawn. = The prisoners were supposed to be executed at dawn.
She was to have been in New York on Thursday. = She was expected to have been there.
I am to be travelling all day tomorrow. = I am expected to be travelling—i.e. I expect to be travelling.
Negatives are a little tricky to paraphrase, because idiomatic use is unsymmetrical:
The prisoners were not to be executed until dawn. = They were not supposed to be executed. BUT
You are not to leave. = You are required not to leave, i.e. You are forbidden to leave.
And the negative passive has an additional possible meaning: BE not to be VERBen can mean BE impossible to VERB. So You are not to be distracted may be understood as either
- You are required not be distracted, i.e., It is forbidden that you be distracted, OR
- You are impossible to distract.
In this case it is clearly the latter which is meant: "I see I cannot distract you."
As was pointed out on that other question you linked, this is a surprisingly tricky sentence!
Let's slowly build it up.
It will take someone else.
What is "it"? Stopping Voldemort again. Implied but never directly said. As for "take", we could say "need" instead, just to be slightly clearer.
[Stopping Voldemort again] will [need] someone else.
This isn't "someone else" as in "we need a different person", but as in "we need other people prepared to do what you did, Harry". When will they be needed? "Next time" (that is, the next time that Voldemort tries to return).
[Stopping Voldemort again] will [need] someone else who is prepared to [do the same as Harry] next time.
Now, Dumbledore is saying that this someone else doesn't have to do much. Hence, it will "merely" (or "only") take someone else. This may sound like it's demeaning Harry's efforts, but it's meant to be reassuring Harry: standing up to Voldemort is not very difficult or unlikely after all, and it doesn't take someone extra-special to do it.
[Stopping Voldemort again] will merely [need] someone else who is prepared to [do the same as Harry] next time.
What, exactly, did Harry do that Dumbledore says they need other people to do (or be prepared to do)? "Fight a losing battle"--or what seems like a losing battle. (Dumbledore omits the word "like", but I'll leave it in for this one example.)
[Stopping Voldemort again] will merely [need] someone else who is prepared to fight a losing battle next time.
[Stopping Voldemort again] will merely [need] someone else who is prepared to fight what seems [like] a losing battle next time.
And now we just replace the bracketed bits with the different wording Dumbledore uses, and we have the sentence (okay, part of a sentence) that you bolded.
It will merely take someone else who is prepared to fight what seems a losing battle next time.
Best Answer
The expression means that you can interpret something in any way you choose. It's an expression used when a situation arises that cannot be easily explained. It may be ambiguous; it may be surprising. It is open to interpretation.
https://english.stackexchange.com/questions/161230/make-of-that-what-you-will-meaning-of-will