What is the threshold in A Wrinkle in Time?

In "A Wrinkle in Time" by Madeleine L'Engle, the threshold represents the boundary between the familiar world and the unknown, where characters must confront challenges and grow. It symbolizes the transition from comfort to adventure, pushing protagonists like Meg Murry beyond their limits. Crossing this threshold is crucial for their development and the overall narrative, as it leads them to discover their strengths and the importance of love and resilience in the face of darkness.