During a trip to Peru, I visited one of the many caves found throughout that mountainous country. Our guide told us that this particular cave had already been explored to a depth of 9 miles—and it went even deeper. We saw fascinating bats, nocturnal birds, and interesting rock formations. Before long, however, the darkness of the cave became unnerving—almost suffocating. I was greatly relieved when we returned to the surface and the light of day.

            That experience was a stark reminder of how oppressive darkness can be and how much we need light. We live in a world made dark…