Light

1.5 This is the message we have heard from him and proclaim to you, that God is light, and in him is no darkness at all.

What is first of all unexpected is that “this is the message”, I would not have expected this, namely that God is the light, to be “the message”. Rather I'd think of the message as "Jesus died for our sins" or "God loves us", God being light doesn't seem to have the punch of something called "the message". Not only so, but I can't remember the last time that someone said to me that "the message" is that God is light. This just isn't part of the evangelical lexicon.
But when I started looking I found not only is this "the message", it is in fact a comprehensive and wonderful message that gives a broad view to what Christ is all about in the world.
First, the message flows back to the beginning of John’s gospel, John 1:4 in him was life,* and the life was the light of men. 5 The light shines in the darkness, and the darkness has not overcome it. John 1:7 He came as a witness, to bear witness about the light, that all might believe through him. 8 He was not the light, but came to bear witness about the light. John 1:9 The true light, which enlightens everyone, was coming into the world.
The whole light deal is not at all odd to John. But what is really telling in all of this is what light is all about. "[Light] enables us to grasp and master the world; to see it is life. Light brings freedom, deliverance, and hope. It is thus an object of praise. It denotes what is publicly known. It accompanies divine manifestations. The light of knowledge brings illumination." Light, then, is the fullness of salvation--freedom, deliverance, an ability to see what is real and master the ways of living in God's good but fallen creation. One last thing on light. Light is what will comes when God returns. God is all about bringing the fullness of light when he brings his new creation in its fullness.
So the message really is that God is light. It's a good thing to hang onto in dark days.