"For you were once darkness, but now you are light in the Lord. Live as children of light..."
Have you ever walked through the valley of the shadow of death? Paul says you are the shadow. Death loomed wherever you went. You were darkness, given over to depraved hearts and minds, and Satan was your lord, the prince of darkness. You who knew not Christ did the bidding of another. But now you are light in the Lord.
Where once you were blind, now you see clearly your condition. Now the the light has come into the world and has exposed what was in the dark. This light brings life, but these days are evil. And Satan cannot touch you. How can he? He only moves about in the darkness, and in the darkest and most remote corners of our heart he wreaks havoc. But just as a fire holds no shadow within it, so to do the children of the light do what Christ does, the first light.
Paul exhorts us to not just to do and obey, but the realize the truth that we are light. We are to grasp that reality by living it. And what does light do? It exposes wrong doing and speaks the truth in righteousness. Remember, one candle which lights another loses neither light nor heat. Embrace your true identity as a child of the light, that light which is God.