For you were once darkness, but now are you light in the Lord: walk as children of light:
Read Chapter 5
Clement Of Alexandria
AD 215
This is the eternal adjustment of the vision, which is able to see the eternal light, since like loves like; and that which is holy, loves that from which holiness proceeds, which has appropriately been termed light. "Once ye were darkness, now are ye light in the Lord."
By darkness is here meant the state of infidelity into which they had been plunged so far as to adore stones as God, and committed without remorse the above-mentioned grievous sins. But delivered by Christ from this darkness, they have become light in the Lord, shining in faith and justice. (Estius)
The darkness is being turned into light. There is not, as some heretics argue, a nature so alienated that it cannot receive salvation…. Those who receive salvation—the righteous—are “the light of the world.” Those who refuse, the unrighteous, are in consequence called darkness…. The difference and distance between one and the other is clearly seen by their own fruits. .
Not, he says, by your own virtue, but through the grace of God has this accrued to you. That is to say, you also were sometime worthy of the same punishments, but now are so no more. Walk therefore as children of light. What is meant however by children of light, he adds afterwards.