The phrase "Speak of the devil, and the devil shall appear" suggests that when someone is talked about, they may unexpectedly show up or become relevant in that moment. This idea is encapsulated in Stephenie Meyer's book "New Moon," where characters confront their fears and relationships in ways that can be surprising and sudden. The act of discussing someone can influence their presence, which adds tension to the narrative.

Meyer uses this concept to explore themes of fate and destiny, illustrating how characters are intertwined through their thoughts and conversations. The unexpected appearances challenge their emotions and decisions, revealing deeper truths about their interactions and the consequences of speaking about one another.