How we cite our quotes: All quotations are from Harry Potter and the Deathly Hallows – Part 2.
Quote #4
NEVILLE: They like punishment, the Carrows.
SOMEONE: They did that to you? Why?
NEVILLE: Today's Dark Arts lesson had us practicing the Cruciatus Curse. On first years. I refused.
When Harry, Hermione, and Ron arrive at Hogwarts to look for a Horcrux, they see that Neville's been roughed up a bit. Turns out two sadists, the Carrows have been running Hogwarts, and they have an appetite for torture and punishment.
Quote #5
HELENA: I know what he's done! I know who he is! He defiled it with Dark magic!
When Harry is trying to find Rowena Ravenclaw's last diadem, he discovers that the ghost of Ravenclaw Tower, Helena (Rowena's daughter), had her own unpleasant run-ins with Voldemort. In fact, Voldemort turned that nice diadem into a Horcrux, which is what Helena means when she says Voldemort "defiled it with Dark magic."
Quote #6
SNAPE: The boy survives. He doesn't need protection; the Dark Lord has gone.
DUMBLEDORE: The Dark Lord will return. And when he does, the boy will be in terrible danger!
Even though Harry spent his early life kinda-sorta protected from Voldemort's evil, Dumbledore knew that Voldy would always come back. So, he tries to enlist Snape to help protect the kiddo from an evil that will be coming straight for him when it returns.