How does Cassandra Clare use imagery in City of Bones?

Imagery:

"The Cup is gone, destroyed by Valentine, just before he died. He set a great fire and burned himself to death along with his family, his wife, and his child. Scorched the land black. No one will build there still. They say the land is cursed."

"Those who die in battle are burned, their ashes used to make the marble arches that you see here. The blood and bone of demon slayers is itself a powerful protection against evil. Even in death, the Clave serves the cause."