Continuing his ″putting off, putting on″ paradigm, Paul contrasts light and darkness. In Christ we are now light (New Testament scholar Peter T. O' Brien notes that at conversion, it is our lives, and not our surroundings, that are changed from darkness to light); we should therefore renounce the darkness that was once inside us (Ephesians 5:8).

Because of our new identity in Christ, we are to walk as children of light by bearing the ″fruit of the light″ (v. 9; the same as the fruit of the Spirit, Galatians 5:22-23). There is no place for the ″fruitless deeds of darkness″ in the Christian's life (Ephesians 5:11). Such disobedient deeds are shameful and we should develop a distaste for them (v. 12).

Light exposes darkness (vv. 13-14), and God's light exposes the sinful deeds of darkness. So we cannot say we don't know about the shameful deeds of darkness. Rather, as we receive the light of Christ that shines on us (v. 14, may be an adapted quotation of Isaiah 60:1 or an early hymn), we are able to unmask dark deeds in us and others. In God's light we can see sin for what it is and stay away from it. The key outcome is: ″Have nothing to do with the fruitless deeds of darkness″ (Ephesians 5:11). Rejecting darkness and putting on light involves finding out ″what pleases the Lord″ (v. 10) and understanding ″what the Lord's will is″ (v. 17). Discovering and doing God's will is central to Christian discipleship. Firstly, it is a sure test that one is a child of God (Mark 3:35; Matthew 7:21; 1 Peter 4:2). Secondly, it involves being ″filled with the Holy Spirit″ (Ephesians 5:18, instead of being drunk with wine-again in line with the idea of ″putting off, putting on″). The Spirit helps us to do God's will. Not knowing God's will is foolishness (v. 17); knowing it but not doing it is equally foolish (Matthew 7:26).

Though we are surrounded by evil, knowing God's will helps us to redeem every good opportunity and live with practical godly wisdom (Ephesians 5:15-16). Sin is not only the wrong that we commit, but also the good that we fail to do when we have an opportunity. We must therefore live carefully (v. 15), not carelessly, so that we will not only know God's will but also follow it every day.