John Chrysostom

Observe how wisely he urges them forward; first, from the thought of Christ, that ye love one another, and do injury to no man; then, on the other hand, from the thought of punishment and hell-fire. "For ye were once darkness," says he, "but are now light in the Lord." Which is what he says also in the Epistle to the Romans; "What fruit then had ye at that time in the things whereof ye are now ashamed?" (Rom. vi. 21), and reminds them of their former wickedness. That is to say, thinking what ye once were, and what ye are now become, do not run back into your former wickedness, nor do "despite to the grace" (Heb. x. 29) of God.

"Ye were once darkness, but are now light in the Lord!"

Not, he says, by your own virtue, but through the grace of God has this accrued to you. That is to say, ye 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.