Ambrosiaster : "Once you were darkness" suggests ignorance. No one sees clearly in shadows. The ignorance referred to is disbelief, harking back to pagan days. Those who lived in darkness have been drawn to faith by the grace of God, which has been brought to light, that is, truth. Things that exist are made apparent in the light. Paganism remains deluded as with covered eyes they celebrate their own mysteries as if in the shadows of a cave. — EPISTLE TO THE Ephesians 5.8 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. — Homily on Ephesians 18 Tertullian : Again to the Ephesians: "Be not, then, partners with them: for ye were at one time darkness." And yet more earnestly: "Communicate not with the unfruitful works of darkness; nay rather withal convict them. — On Modesty