In this brief but profound essay Lewis uses a simple analogy to differentiate between two valid and complementary ways of knowing: looking at a beam of light and looking along it. He famously says, “I believe in Christ as I believe the sun has risen: not only because I see it, but because by it I see everything else.”
I was standing today in the dark toolshed. The sun was shining outside and through the crack at the top of the door there came a sunbeam. From where I stood that beam of light, with the specks of dust floating in it, was the most striking thing in the place. Everything else was almost pitch-black. I was seeing the beam, not seeing things by it.
Then I moved, so that the beam fell on my eyes. Instantly the whole previous picture
vanished. I saw no toolshed, and (above all) no beam. Instead I saw, framed in the irregular cranny at the top of the door, green leaves moving on the branches of a tree outside and beyond that, 90 odd million miles away, the sun. Looking along the beam, and looking at the beam are very different experiences