1 John 1:5
5 This then is the message which we have heard of [from] Him [Christ], and declare to you, that God is light, and in Him is no darkness at all.
John was one of the original 12 disciples. In fact, he was in the inner circle of three disciples—Peter, James, and John. He had been with Jesus most of the three years of His ministry and had heard Jesus teach. I don’t think John is saying this is the only message because in 1 John 3:11 he says, “For this is the message that you heard from the beginning, that we should love one another” (1 John 3:11).
I think what John is emphasizing is the message or proclamation of Jesus that fits the idea he trying to get across. God is light and not darkness. John began the Gospel of John.
“4 In Him was life; and the life was the light of men. 5 And the light shines in darkness; and the darkness comprehended it not. 6 There was a man sent from God, whose name was John [the Baptist]. 7 The same came for a witness, to bear witness of the Light, that all men through Him might believe. 8 He was not that Light, but was sent to bear witness of that Light. 9 That was the true Light, which lights every man who comes into the world” (John 1:4-9).
As John wrote in John 8:12 concerning what Jesus said, “I am the light of the world: he that follows Me shall not walk in darkness, but shall have the light of life.”
The message is that there are to states of man. They are either in darkness. They are ignorant or willfully rejecting the light. This is the man who has no hope and no life.
The other state is following the Light. I think King James got it right when the capitalized Light when it meant the person of Jesus. When a person accepts Jesus as their Savior and Lord, God translates them from darkness to light. “12 Giving thanks to the Father, who has made us meet to be partakers of the inheritance of the saints in light: 13 Who has delivered us from the power of darkness, and has translated us into the kingdom of His dear Son:” (Colossians 1:12-13).
God is light and no darkness not at all, ever.