City of Bones
How we cite our quotes:
"It's their job, Clary," [Simon] said gently. "Fighting demons--it's what they do. Not what you do." (19.104)
Having a duty gives the Shadowhunters a purpose, and Clary feels lost without a purpose of her own. No wonder she jumps on their bandwagon so quickly. And wanting to get her mother back didn't hurt the cause either.
"I may not believe in sin," [Jace] said, "but I do feel guilt. We Shadowhunters live by a code, and that code isn't flexible: Honor, fault, penance, those are real to us, and they have nothing to do with religion and everything to do with who we are. This is who I am, Clary." (19.122)
Jace's job defines him. Talk about a workaholic.
"Faithful unto death." (22.89)
Here, Luke is translating the NYPD motto, Fidelis ad Mortem, for Clary. It echoes the Shadowhunter motto, don't you think?