Dumbledore answers Harry's questions

'Sir, there are some other things I'd like to know, if you can tell me... things I want to know the truth about...'
'The truth.' Dumbledore sighed. 'It is a beautiful and terrible thing, and should therefore be treated with great caution. However, I shall answer your questions unless I have a very good reason not to, in which case I beg you'll forgive me. I shall not, of course, lie.'
'Well... Voldemort said that he only killed my mother because she tried to stop him killing me. But why would he want to kill me in the first place?'
Dumbledore sighed very deeply this time.
'Alas, the first thing you ask me, I cannot tell you. Not today. Not now. You will know, one day... put it from your mind for now, Harry. When you are older... I know you hate to hear this... when you are ready, you will know.'
And Harry knew it would be no good to argue.

'But why couldn't Quirrell touch me?'
'Your mother died to save you. If there is one thing Voldemort cannot understand, it is love. he didn't realise that love as powerful as your mother's for you leaves its own mark. Not a scar, no visible sign... to have been loved so deeply, even though the person who love us is gone, will give us some protection for ever. It is in your very skin. Quirrell, full of hatred, greed and ambition, sharing his soul with Voldemort, could not touch you for this reason. It was agony to touch a person marked by something so good.'

'And there's something else... Quirrell said Snape -'
'Professor Snape, Harry.'
'Yes, him - Quirrell said he hates me because he hated my father. Is that true?'
'Well, they did rather detest each other. Not unlike yourself and Mr Malfoy. And then, your father did something Snape could never forgive.'
'What?'
'He save his life.'
'What?'
'Yes...' said Dumbledore dreamily. 'Funny, the way people's minds work, isn't it? Professor Snape couldn't bear being in your father's debt... I do believe he worked so hard to protect you this year because he felt that would make him and your father quits. Then he could go back to hating your father's memory in peace...'

THE MAN WITH TWO FACES - Pg 322