Throughout the Old and New Testaments, including the writings of John, the theme of light is used in three ways.

First, light designates an essentially moral reality, a manner of upright living. John seldom uses the image of light in this sense. Except for a rare text, such as John 3:20, he is much too occupied with Christ as the light.

Second, light designates an extrinsic rule of conduct, a norm for human actions. This is the usual way of referring to the Mosaic Law in the Old Testament.

Third, light designates Christ as the Messiah bringing salvation to those sitting in darkness or death. This third theme John employs in his frequent use of the world light. He applies it to Christ in His function as Savior, God’s healing power among His children who live in darkness or the lack of God’s life.

Christ in John’s Gospel calls Himself the Light of the world, meaning primarily the one sent by God, who is God also, to bring us salvation: I am the light of the world. He who follows me will not walk in the dark but have the light of life. Also, I have come into the world as a light, so that no one who believes in me might remain in darkness.

In the Prologue of his Gospel, St. John presents God’s Word as Life that gives light or salvation. But sin has disrupted the plan of God. Not only mankind but the entire world is immersed in darkness. It is more than a mere absence of light. The darkness possesses an inimical force that rises up to extinguish the light. But already in the Prologue St. John predicts the victorious outcome of the Light conquering the darkness. The light shines in the darkness, and the darkness did not lay hold of it.

Nonetheless the fact that human beings failed to receive the Light did not lessen Christ’s activity. He still remained the true light. Only Jesus Christ, not John the Baptist or anyone else, is the true light that illuminates all men. He is the true light because He is the Son of God, the true Messiah, the Anointed One, who brings eternal life and truth to all who accept Him, His teachings and His person.

By use of the rich symbol of light, John pictures Christ not only as an illuminator, a teacher, but as the one who actually effects salvation. He who follows me does not walk in darkness but will have the light of life. The Light is at one and the same time the effect and the cause of the life.