For ye were sometimes darkness, but now are ye light in the Lord: walk as children of light:

For you were heretofore darkness, but now light in the Lord. Walk then as children of the light.

For ye were sometime darkness, but now are ye light in the Lord: walk as children of light;

for ye were once darkness, and now light in the Lord; as children of light walk ye,

There was a time when you were nothing but darkness. Now, as Christians, you are Light itself.

For you at one time were dark, but now are light in the Lord: let your behaviour be that of children of light

For, although you were once in darkness, now, by your union with the Lord, you are in the light. Live as children of light –

Eratis aliquando tenabrae; nunc autem lux in Domino; tanquam filii lucis ambulate;

For ye were once darkness. The precepts which immediately follow derive greater weight from the motives with which they are mingled. Having spoken of unbelievers, and warned the Ephesians not to become partakers of their crimes and their destruction, he argues still further, that they ought to differ widely from the life and conduct of those men. At the same time, in order to guard them against ingratitude to God, he refreshes their remembrance of their own past life. "You ought," he says, "to be very different persons from what you formerly were; for out of darkness God hath made you light." Darkness is the name here given to the whole nature of man before regeneration; for, where the brightness of God does not shine, there is nothing but fearful darkness. Light, again, is the name given to those who are enlightened by the Spirit of God; for immediately afterwards in the same sense, he calls them children of light, and draws the inference, that they ought to walk in light, because by the mercy of God they had been rescued from darkness. Observe here, we are said to be light in the Lord, because, while we are out of Christ, all is under the dominion of Satan, whom we know to be the Prince of darkness.

For ye were sometimes darkness - see the Ephesians 2:11-12 notes; 1-Corinthians 6:11 note. The meaning here is, that they were themselves formerly sunk in the same ignorance, and practiced the same abominations.
But now are ye light in the Lord - Light is the emblem of happiness, knowledge, holiness. The meaning is, that they had been enlightened by the Lord to see the evil of these practices, and that they ought, therefore, to forsake them.
Walk as children of light - see the notes on Matthew 1:1, on the use of the word "son," or "children." The meaning here is, that they should live as became those who had been enlightened to see the evil of sin, and the beauty of virtue and religion; compare John 12:36, where the same phrase occurs.

For ye were sometimes (ποτε, formerly) darkness - While ye lived in darkness, ye lived in these crimes.
But now are ye light in the Lord - When ye were in heathenish darkness ye served divers lusts and pleasures, but now ye have the light - the wisdom and teaching which come from God; therefore walk as children of the light - let the world see that ye are not slaves to the flesh, but free, willing, rational servants of the Most High; not brutish followers of devil gods.

For ye were sometimes darkness, but now [are ye] (c) light in the Lord: walk as children of light:
(c) The faithful are called light, both because they have the true light in them which enlightens them, and also because they give light to others, insomuch that their honest conversation reproves the life of wicked men.

For ye were sometimes darkness,.... Not only dark, but darkness itself; exceeding blind, dark, and ignorant, respecting spiritual things; so the Gentiles were wont to be called by the Jews, "darkness" (k) itself; of this darkness; see Gill on Ephesians 4:18.
But now are ye light in the Lord; either in, or by the Lord Jesus Christ, the light of men, from whom all spiritual light comes; or by the Lord the Spirit, by whom the eyes of their understandings were enlightened, to see the exceeding sinfulness of sin, in heart and life; the insufficiency of their own righteousness and moral virtues, to justify them before God; and the true and right way of righteousness, life and salvation by Christ; and to have some light into the several doctrines of the Gospel, and even a glimpse of the invisible glories and realities of another world: and this light is so great, that they are not only said to be enlightened, but to be light itself; and this they have not of, and from themselves, but the Lord; and therefore should
walk as children of light; not in sins, which are works of darkness, but in faith, truth, and holiness.
(k) Tzeror Hammor, fol. 1. 2.

sometimes--"once." The emphasis is on "were." Ye ought to have no fellowship with sin, which is darkness, for your state as darkness is now PAST. Stronger than "in darkness" (Romans 2:19).
light--not merely "enlightened"; but light enlightening others (Ephesians 5:13).
in--in union with the Lord, who is THE LIGHT.
children of light--not merely "of the light"; just as "children of disobedience" is used on the opposite side; those whose distinguishing characteristic is light. PLINY, a heathen writing to Trajan, bears unwilling testimony to the extraordinary purity of Christians' lives, contrasted with the people around them.

Ye were once darkness. Not only lived in darkness, but gave off no light and darkened others.
Now are ye light. Shining with the light that comes from Christ.
For the fruit of the Spirit. To walk as children of light is to bear the fruit of the Spirit. This is shown by goodness and righteousness. See Galatians 5:22.
Proving. Showing by walking in the light what is acceptable to God.

Ye were once darkness - Total blindness and ignorance. Walk as children of light - Suitably to your present knowledge.