What does Ephesians 5:8 mean?

Paul contrasts the past of his readers with their current status. Before knowing Christ, all human beings are in "darkness." As believers, they are instead "light in the Lord." The contrast of dark/light is as old as Genesis 1 and is commonly associated with evil versus good, exactly as Paul uses it in this context.

Based on their new status, Paul commands his readers to, "Walk as children of light." Paul uses this phrase in one other passage, 1 Thessalonians 5:5, where he describes Christians as "children of light, children of the day. We are not of the night or of the darkness." In that passage, the emphasis is on living "awake," being alert to obey the Lord. This is a theme Paul will again note in Ephesians 5:14. Paul's similar application here is to live in obedience as believers. Christians are to imitate God (Ephesians 5:1), walk in love (Ephesians 5:2), and flee from sinful actions (Ephesians 5:3–6). They should not live like unbelievers or be "partners" with them (Ephesians 5:7).