Words are, in my not-so-humble opinion, our most inexhaustible source of magic. Capable of both inflicting injury, and remedying it.
— J. K. Rowling
Tempting Dumbledore Inspirational quotations
You will also find that help will always be given at Hogwarts to those who ask for it.

Do not pity the dead, Harry. Pity the living, and, above all those who live without love.

To have been loved so deeply, even though the person who loved us is gone, will give us some protection forever.
The consequences of our actions are always so complicated, so diverse, that predicting the future is a very difficult business indeed.
Dumbledore says people find it far easier to forgive others for being wrong than being right.

Do not pity the dead, Harry.
I believe your friends Misters Fred and George Weasley were responsible for trying to send you a toilet seat. No doubt they thought it would amuse you.
It was important, Dumbledore said, to fight, and fight again, and keep fighting, for only then could evil be kept at bay, though never quite eradicated. . . .

Curiosity is not a sin.... But we should exercise caution with our curiosity... yes, indeed.
It is the unknown we fear when we look upon death and darkness, nothing more.
One can never have enough socks," said Dumbledore.
"Another Christmas has come and gone and I didn't get a single pair. People will insist on giving me books.

Dark times lie ahead of us and there will be a time when we must choose between what is easy and what is right. -Albus Dumbledore
You think the dead we loved truly ever leave us? You think that we don't recall them more clearly in times of great trouble?
I seem to remember telling you both that I would have to expel you if you broke any more school rules,” said Dumbledore. Ron opened his mouth in horror. “Which goes to show that the best of us must sometimes eat our words,” Dumbledore went on, smiling.

Which only goes to show that the best of us must sometimes eat our words,' Dumbledore went on, smiling.