“You might ask—and with good reason—why it had to be so. Why could some wizarding family not have taken you in? Many would have done so more than gladly, would have been honoured and delighted to raise you as a son.
“My answer is that my priority was to keep you alive. You were in more danger than perhaps anyone but I realised. Voldemort had been vanquished hours before, but his supporters—and many of them are almost as terrible as he—were still at large, angry, desperate and violent. And I had to make my decision, too, with regard to the years ahead. Did I believe that Voldemort was gone for ever? No. I knew not whether it would be ten, twenty or fifty years before he returned, but I was sure he would do so, and I was sure, too, knowing him as I have done, that he would not rest until he killed you.
“I knew that Voldemort’s knowledge of magic is perhaps more extensive than any wizard alive. I knew that even my most complex and powerful protective spells and charms were unlikely to be invincible if he ever returned to full power.
“But I knew, too, where Voldemort was weak. And so I made my decision. You would be protected by an ancient magic of which he knows, which he despises, and which he has always, therefore, underestimated—to his cost. I am speaking, of course, of the fact that your mother died to save you. She gave you a lingering protection he never expected, a protection that flows in your veins to this day. I put my trust, therefore, in your mother’s blood. I delivered you to her sister, her only remaining relative.”
“She doesn’t love me,” said Harry at once. “She doesn’t give a damn—”
“But she took you,” Dumbledore cut across him. “She may have taken you grudgingly, furiously, unwillingly, bitterly, yet still she took you, and in doing so, she sealed the charm I placed upon you. Your mother’s sacrifice made the bond of blood the strongest shield I could give you.”
“I still don’t—”
“While you can still call home the place where your mother’s blood dwells, there you cannot be touched or harmed by Voldemort. He shed her blood, but it lives on in you and her sister. Her blood became your refuge. You need return there only once a year, but as long as you can still call it home, whilst you are there he cannot hurt you. Your aunt knows this. I explained what I had done in the letter I left, with you, on her doorstep. She knows that allowing you houseroom may well have kept you alive for the past fifteen years.”