Papa was Nan’s favorite name for God, and it expressed her delight in the intimate friendship she had with him.
-- Narrator (Chapter 1: A Confluence of Paths)

Importance: The quote explains why it was so disturbing that the note that Mack received in his mailbox was so disturbing to him. The signature “Papa” indicates the letter might have been from God since it was a familiar name the family, especially Nan, used for God. The nickname for father indicates a very close and personal relationship with one’s father, a relationship that Nan believed she had with God.

Shortly after the summer that Missy vanished, The Great Sadness had draped itself around Mack’s shoulders like some invisible but almost tangibly heavy quilt.
-- Narrator (Chapter 2: The Gathering Dark)

Importance: Mack calls the depression that surrounded him after Missy’s abduction and murder The Great Sadness. The author uses a simile to compare Mack’s depression to a heavy quilt that weighted him down...