What a sentence is contained in verse 5! God is Light, and in Him there is no darkness at all.
This is a forceful and clear parallelism. John tells us what he means and then tells us what he does not mean. Every great positive truth of the Bible has its negative implication. If Jesus Christ is Lord, then I am not Lord. If God is filled with light then He is not filled with darkness.
The word light is used interchangeably by John in this letter and in his Gospel for the word truth. (See John 1:9, John 1:14 and 1 John 1:6.) What John means by 'light' and 'truth' is that his teaching is rooted more in the Old Testament understanding of 'light' and 'truth' than in the Greek philosophical understanding of these concepts. We need to closely examine the way that the teaching about light and truth in both the Gospel of John and 1 John is developed.
In the OT, 'light' has to do with finding the path. The people who walked in darkness have seen a great light (Isaiah 9:2). Your word is a lamp to my feet and a light to my path (Psalm 119:105). These texts show the basic connection that is present in the OT between light from God and showing His people the way for their feet. Light is also connected in the OT to an even more fundamental discovery, and that is the discovery of the character and nature of God by His people. For instance, Psalm 27 tells of David's discovery not only of the way, but of God Himself in the midst of David's trial. David had found the face of the Lord. He begins this psalm, The Lord is my light and my salvation; whom shall I fear? (Psalm 27:1). Likewise the text in Isaiah 9 moves from the pathway language to the intensely personal hope, For unto us a Child is born …" (Isaiah 9:6).
The Lord's summation of the great I AM sentences in John's Gospel is also set into this Old Testament way of thinking about light and truth. I am the way, and the truth, and the life; no one comes to the Father, except through Me (John 14:6). Note that this is the language of the roadway and the language of personal encounter with the Father. We find the way in the truth that is Jesus Christ, and because of that way we find the very source of light and life, who is God Himself. Psalms 27 and 119 are now fulfilled in this encounter with Jesus of Nazareth!
John has the same roadway and interpersonal, encounter mindset in his own thinking as he tells his readers about God. This will be made clear as the verses unfold in 1 John 1:5-10.
John announces the liberating news that God is not only the source of life but also of light, of truth. John dares to commit God to the way of light. God never deceives, misleads, and distorts. There can be no strategy of heavenly deception on God's part, because God is Light and His own character, His own essential nature, rejects such a strategy. God is not the prince of lies but the One who reveals and shows the way. Darkness hides and confuses pathways, but light makes the faces recognizable and the outline of the roadway discernible.
But, and this is important, it is not John who has created this message about God. John tells us that it is the message which he heard from God's speech. John has not really committed God to the way of truth, instead he has announced like a trumpeter this good news about God which God himself has already made known. God has spoken for Himself, and we have learned from the first five verses of 1 John that His speech is the speech of Life and of Light.
John's affirmation is the promise that God's self-disclosure is on the side of truth, and therefore when Jesus Christ is Lord of our life, we then see the road more clearly. Jesus Christ not only shows us who the Father is, He also shows us who we are and where we are. We see better our own faces and we see better the landscape. He is the Light who makes the roadway upon which we live and move and have our being come into focus. As C.S. Lewis once wrote in Miracles: We believe that the sun is in the sky at midday in summer not because we can clearly see the sun (in fact, we cannot) but because we can see everything else.
I believe that one way to test the worthiness of a person's world-view or religious claim is to ask the question: 'Does this world-view bring all of the parts of the puzzle of my life and world together?' Are the separate pieces that make up normal existence integrated so that each is meaningful and in clear focus when seen through the lens of this world-view? Jesus Christ as Lord and center of our lives makes sense of the parts just as He makes sense of the core. This is the characteristic of light. It is like a lamp unto our feet.