God is light, and in Him is no darkness at all, John tells us.
What might that mean?
God is an eternal fellowship of light, eternal source, eternal radiance, and eternal dispersion that illumines the source and radiance.
Light gives life. Nothing can live without light. To say that God is light is to say that He gives life to everything. If God is eternal light, then God is eternal life. God cannot live without light, because God cannot live without Himself. “God is light” means that God is life in Himself. To say that God is light is to speak of God’s aseity. We can unravel this Trinitarianly: The Father cannot live without the Son and Spirit, nor the Son without the Father and Spirit, nor the Spirit without the Father and Son.
Light keeps time. The rhythm of light and darkness marks out days. The movements of sun, moon, and stars mark months, seasons, years.
Light is the future. The pattern of creation is darkness to light, first darkness broods over the deed, then the fiat lux. Days begin with evening, and history begins in the dusk of the old creation. Light comes last, and if God is light, He is the God of future, the light that glows ahead and shines back to illumine all that comes before.
God creates light. The first thing created is light, and with the creation of light, God gives everything else to us. Without light, no living thing could live; without light, even inanimate things have no visibility, and so none of their glory. Maybe things could exist in a world completely shrouded in darkness, but such a world would be little better than a world tohu wbohu, formless and empty. If God is light, and creates light, and if everything that is in light is light (Ephesian 5:13), then the whole creation gleams with the light of God refracted through created things.
Light exposes what’s hidden, and so light makes judgment possible. Exposure is judgment, and so God is light also in the sense that He is Judge, the one who sees in secret.
Light is glorious; it dazzles. It is glory. It also glorifies because it enables other things to emerge in the fullness of their own glory. Since God is light, God is the glory and the glorifier of all things. The Father is the Light that makes the Son radiant in the Spirit. The Triune communion is an eternal, mutual, exchange of light.
Light is good, the first created good, the good without which nothing else could be or be good.
Light repels those who want to keep their evil deeds hidden; light attracts those who practice the truth, because they want their deeds manifested as God’s own works.
Light conquers darkness. God is light because He overcomes: He is victor.