Everyone does what they must to survive. In that way even we are just like humans.
-- Rafael (Chapter 19 paragraph 22)

Importance: Raphael says this to Simon as he tries to convince him to submit to the vampires and allow them to kill him because he can stand in the daylight where other vampires cannot.

The smoke rose in a lazy spiral, tracing delicate lines of black across the clear air. Jace, alone on the hill overlooking the cemetery, sat with his elbows on his knees and watched the smoke drift heavenward. The irony wasn’t lost on him: These were his father’s remains, after all.
-- Jace (Epilogue paragraph 1)

Importance: This is Jace's reaction to watching his father's funeral. Jace finds it ironic that Valentine's funeral pyre is admitting smoke to heaven because Valentine was evil, and his spirit should be going the other direction.

My mom got the spell that put her in this state from a warlock...
-- Clary (Chapter 1 paragraph 24)