Your eye is the lamp of your body. When your eyes are good, your whole body also is full of light. But when they are bad, your body is full of darkness. — Luke 11:34

When your eye is single, your whole body is full of light. The natural person doesn't accept the things of the Spirit — they're folly to him. We need God to open our eyes to behold wonderful things in His Word. Jesus is the light of the world, and as we behold His glory, we're transformed into the same image. God who said'Let light shine out of darkness' has shone in our hearts to give the light of the knowledge of His glory in the face of Christ.