God is light, and Christ is the image of the invisible God; God of gods, Light of lights. Christ in calling himself the light expresses, (1) What He is in Himself – most excellent and glorious. (2) What He is to the world – the fountain of light, enlightening every man. What a dungeon would the world be without the sun! So would it be without Christ by whom light came into the world (Joh 3:19).
Commentary from Matthew Henry’s “Commentary on the Whole Bible”