John is so subtle that we nearly miss it. Jesus says, “While I am in the world, I am the light of the world” (John 9:4), implying that at some time he might not be in the world. Then he heals a blind man with clay and tells him to go wash (9:5).
When the blind man comes back seeing, Jesus isn’t there. But it’s not until verse 12 that we realize this: “They said to the blind man, ‘Where is Jesus?’ He said, ‘I don’t know.’” Between verses 5 and 12, the Light has gone.
Jesus doesn’t say here than when He, the Light, leaves, He will leave light behind Him. His actions speak loudly enough, because He heals the blind man by “anointing” him with clay. Jesus the light exits the story, but He’s left a lit lamp behind, a man once blind who now sees.
That man shines into the darkness of Jesus’ enemies, and John’s earlier warning is proven once again: Men love darkness rather than light because their deeds are evil. Later, they think they can snuff the light by snuffing Jesus. But He’s been busy preparing lamps and wicks, and promises that after He leaves for good, He will send down the fire of the Spirit to light them, so they will be lights, like the man born blind.
This is why the light can’t be put out. When one goes out, there are a thousand more left behind.