But if we walk in the light, as he is in the light, we have fellowship with one another, and the blood of Jesus Christ, his Son, cleanses us from all sin.

 (iv) It tells us of the guidance of God. It is one of the great functions of light to show the way. The road that is lit is the road that is plain. To say that God is light is to say that he offers his guidance for the footsteps of men. 