What does the Harbinger represent in the novel, Hold Me Closer, Necromancer?

The Harbinger symbolizes a bridge between two worlds - the living and the dead. A Harbinger is a guide that transports souls to the afterlife. When the Harbinger arrives it connects Sam with the afterlife, confirming, not its specifics, but its existence. Sam’s ability to see Ashley the Harbinger without dying demonstrates how Sam exists as part of both worlds.