While the Clave disapproves of trespassers, oddly they take an even darker view of beheading and skinning people. They're peculiar that way.”
-- Will (chapter 2)

Importance: Will is talking to the Dark Sisters who are trying to argue that he cannot be in their house. This is the first mention of the Clave, which is the body that rules over the Shadowhunters, and shows that there is a set of rules that guide the actions of the Shadowhunters and the Downworlders. The fact that Will can be so flippant at a time like this is an ingrained part of his character.

What if one of the times I Changed, when I turned back into myself, I didn't do it quite right? What if this isn't even my true face?”
-- Tessa (chapter 3)

Importance: Tessa's identity is one of the novel's themes, and she often struggles with the fact that she does not know what she is. At this...