Don’t participate in the things these people do. For once you were full of darkness, but now you have light from the Lord. So live as people of light! For this light within you produces only what is good and right and true.
Ephesians 5:7-9 NLT
The Christian’s walk, their progress toward heaven, should be characterized by unity (Eph 4:1-16), by purity (4:17-28), by love (4:29-5:1), and now, by light.” Paul says we should “walk as children of light” (“live as people of light” above).
Why does he use that phrase “children of light.” I think he wants to stress that a walk that is filled with light is not merely a matter of choice and effort. We are by nature “children of darkness.” Light shines outward, giving life, but we, like the “black holes” of space, suck everything in, killing it in the process. That is not changed by trying, it is changed miraculously. Through Christ, we are born into a new kingdom, the kingdom of light, and the fruit of that change is “good, and right and true” (Eph 5:9) Light has given birth to us, it has come into us and will as a matter of course shine out of us. So John can say in his first letter, “we are lying if we say we have fellowship with God but go on living in spiritual darkness.”
So what is “spiritual darkness”? Paul has been talking about it in several different ways ever since 4:1. It is to live for oneself, to live as though satisfying desire is the only purpose of life; it is to talk crudely and harshly, tearing others down rather than building them up; it is to want what others have and foolishly imagine we would be happy if we had it; it is think, talk and act perversely, contrary to God’s directions for life. To walk as children of light is to do the exact opposite of these, allowing the light of God that he has placed within us to shine out beneficially on all with whom we come in contact.
Called To Be Transformed 