In this passage, Victor Hugo reflects on the duality of shadows and light as symbols of potential and transformation within early Christianity. He suggests that shadows hold dormant energy, waiting for the right moment to ignite change. The imagery of volcanic eruptions conveys how hidden forces can erupt into brilliance, signifying that beginnings often emerge from darkness.

The catacombs, where the first mass was conducted, represent more than just a burial place; they symbolize a universal foundation for faith and hope. Hugo implies that these sacred spaces contain the essence of a transformative light capable of changing the world, indicating that out of darkness can arise great illumination and enlightenment for humanity.