 | The eye is the lamp of the body. If your eyes are good, your whole body will be full of light. |
 | The light of the body is the eye: if therefore thine eye be single, thy whole body shall be full of light. |
In the middle of His teaching about the dangers of serving two masters and storing up treasures on Earth, Jesus used this analogy to help explain the importance of what to focus your eyes and your life on.
It is through the eye that the body can see. If the eye is good, the whole body is flooded with light. But if the eye is bad, then vision is impaired and filled with darkness.
He went on to say that if we fill our life with His teachings, light will flood our lives. We will serve Him and not money, and we will store up treasures in Heaven alone.
Jesus knows that our true security is in Him. In knowing that, he urges us to flood our lives with His light, pushing out all crevasses of darkness.