The implication of the wording "once you were full of darkness" implies that this is true of every believer's past. That was the experience we all had. But it is not to be our present experience. Once we were in darkness. Now we are in the light. As John Newton said in his great hymn, Amazing Grace: "I once was lost but now I'm found, was blind, but now I see." Jesus is the Light of the Word, John 8:12. He came to give light so all who lived in darkness could finally see God as their Creator and Christ as their Redeemer. Once the "light came on" the new believer begins to live as they were meant to live. They are no longer to live as those who grope around in the dark!
As "people of light" we not only enjoy the Light shining in us, but we also let this wonderful Light shine through us. We are not in darkness in our souls, but we do live in a world of darkness. Our goal is to be a light for the world to see Christ in us and to lead people out of darkness. How clear is your light shining today?