“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 also is full of darkness. See to it, then, that the light within you is not darkness. Therefore, if your whole body is full of light, and no part of it dark, it will be completely lighted, as when the light of a lamp shines on you.”
A blind person is unable to receive light through their eyes, so their world is dark, without color, form or shape. When we were without Christ it was the same. Our spiritual man was unable to receive the light of truth, and we were in darkness of sin. When Christ comes into our hearts through salvation, the darkness of sin is washed away, and the light of truth fills us with light from the inside out. Look at verse 36 again. If we are so lighted, we cannot help but draw others to Christ.