Harley was momentarily confused by the old man's words, but instinctively replied, "Thank you for the compliment, Professor Dumbledore."
"You shouldn't thank me. You should thank yourself.
"Next, I'm going to introduce you to a kind of magic." Professor Dumbledore's tone was complicated, his face seeming to show both reminiscence and regret.
He waved a hand lightly. The golden flames on the Diary slowly faded, then disappeared.
But nothing unusual appeared on the Diary. It seemed like an ordinary diary—innocent, pitiful, and completely harmless.
"A Horcrux. An extremely evil form of Dark Magic." Dumbledore's expression was grave, but he wasn't watching the Diary. He was watching Harley's face.
"This magic allows someone to hide a portion of their soul inside an object.
"As long as that object isn't destroyed, its creator won't die even if their body is damaged or destroyed.
"That's because part of their soul remains in the world, unharmed.
"Furthermore, after their original body is gone, the soul in either their body or the Horcrux can absorb magic and life force from the outside world and resurrect.
"Of course, a Horcrux can also grant someone a form of immortality. If their body grows too old, they can rely on the soul inside the Horcrux to sustain their life.
"After all, the time of that separated fragment of the soul is effectively frozen, so the person's original self can't die either.
"Even if both their soul and body rot away completely, they still can't die.
"Of course, to successfully make a Horcrux, you have to kill someone.
"Only by maliciously murdering an innocent life and using a special incantation can you split your soul.
"Then you have to use other special incantations to permanently preserve the separated soul in the Horcrux's vessel."
Professor Dumbledore stopped explaining and watched