Quote 4
"You are the true master of death, because the true master does not seek to run away from Death. He accepts that he must die, and understands that there are far, far worse things in the living world than dying." (35.88)
Dumbledore explains the real meaning of "master of death" here – it doesn't mean that Harry commands Death, but rather that he's kind of on equal terms with it. Like the third brother in the story (his ancestor), he's willing to approach Death face-to-face when the time is right, and thus has a greater understanding of it… or, rather, has come to an understanding with it.
Quote 5
"But this is touching, Severus," said Dumbledore seriously. "Have you grown to care for the boy, after all?"
"For him?" shouted Snape. "Expecto Patronum!"
From the tip of his wand burst the silver doe: She landed on the office floor, bounded once across the office, and soared out of the window. Dumbledore watched her fly away, and as her silvery glow faded he turned back to Snape, and his eyes were full of tears.
"After all this time?"
"Always," said Snape. (33)
Snape's finest quality – his loyal love for Lily – informs the most intimate part of himself, his Patronus.
Quote 6
"Yes, we have been given power and yes, that power gives us the right to rule, but it also gives us responsibilities over the ruled. We must stress this point, it will be the foundation stone upon which we build… where we meet resistance, we must use only the force that is necessary and no more." (18.34)
This quote, from a letter that young Dumbledore wrote to Grindelwald, demonstrates the dangers of having too much power – the idea that the added strength of magic makes wizards fit to rule (albeit "responsibly") over Muggles is the overly enthusiastic and dangerously idealistic claim of an immature, young wizard.