Albert Barnes Commentary Ephesians 5:8

"For ye were once darkness, but are now light in the Lord: walk as children of light" — Ephesians 5:8 (ASV)

For you were sometimes darkness. (See Ephesians 2:11, Ephesians 2:12; 1 Corinthians 6:11.)

The meaning here is that they were themselves formerly sunk in the same ignorance and practiced the same abominations.

But now you are light in the Lord. Light is the emblem of happiness, knowledge, and 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 Matthew 1:1 regarding the use of the words "son" or "children".) The meaning here is that they should live as was fitting for 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.)