The light of the body is the eye: if therefore thine eye be single, thy whole body shall be full of light. But if thine eye be evil, thy whole body shall be full of darkness. If therefore the light that is in thee be darkness, how great is that darkness!
Jesus realized that it would be difficult for His followers to see how His unconventional teaching on security for the future could possibly work. So He used an analogy of the human eye to teach a lesson on spiritual sight. He said that the eye is the lamp of the body. It is through the eye that the body receives illumination and can see. If the eye is good, the whole body is flooded with light. But if the eye is bad, then vision is impaired. Instead of light, there is darkness. The application – the good eye belongs to the person whose motives are pure, who has a single desire for God’s interests, and who is willing to literally accept Christ’s teachings. Their whole life is flooded with light. They believe Jesus’ words, forsake earthly riches, lay up treasures in heaven, and they know that this is the only security. We are to be sure that we are “single eyed”.