Here are the contexts of the quotes tweeted from October 9 through October 15, 2014. All but the last are from The Two Towers, by JRR Tolkien.
“Perilous to us all are the devices of an art deeper than we possess ourselves.” Gandalf, discussing how the palantir may have led to Sauruman’s downfall.
“If we kill him, we must kill him outright.” Frodo, after they have captured Gollum.
“What he means to do is another matter.” Frodo, still considering what to do with Gollum.
“Now that I see him, I do pity him.” Frodo, replying to his memory of Gandalf’s words about Gollum, back in the Shire. (It was the Shire in the book, though the speech was moved to Moira in the movie.)
“Just try and stop me.” Sue Ann Bowling, Homecoming. Marna’s response to Lai’s suggestion that they take in Roi.