“The lamp of your body is your eye. When your eye is single, your whole body also is full of light, but when it is evil, your body also is full of darkness.”
And how do we light that lamp? The light comes to us from God and from the Lord. And it comes through the window of the eye, which is itself thus like a lamp, for it enables light to shine into our lives. If our eye is single-minded and fixed on Him and His word then our whole body will be full of light. We will be filled with truth and goodness and righteousness and holiness and His light will continually shine into our hearts. We will walk in the light as He is in the light (1 John 1:7), as indeed He is the light (1 John 1:5; John 8:12). But the eye of anyone turns away from Him and His word, and ceases to be single, then the light will be cut off and darkness will fill their lives. The evil of unbelief and disobedience will have possessed them. They will walk in darkness. And their whole lives will be filled with darkness.