The resumptive inferential particle translated "Therefore"marks the beginning of a new paragraph in Paul's thought (cf. 4:1, 17; 5:1, 15). He related three commands concerning walking (living) in the light in these verses and added reasons and explanations to motivate and to assist his readers.
5:7 It is inconsistent for the objects of God's love (v. 2) to become fellow partakers (3:6) with the objects of God's wrath (v. 6) by joining in selfish, immoral, impure conduct. This verse contains the first command.
5:8 The reason Christians should not partake with unbelievers in their evil deeds is that we were formerly darkness (cf. 4:17-19) but are now light having trusted Jesus Christ (2:1-3; 3:17-24; cf. Matt. 5:14; Col. 12:1-13). The second command is to walk as children of light. Obviously it is possible for the children of light not to walk (live) as children of light. Otherwise the command would be unnecessary.
5:9 The fruit of the light is those qualities that characterize God's life (i.e., the fruit that the Spirit produces). The three qualities mentioned here are the opposite of the fruit of darkness (4:18-19). If the child of light does not walk in the light, he will not bear much of the fruit of the light (cf. John 15:1-6). He might even be outwardly indistinguishable from a child of darkness (cf. Matt. 13:24-30).
5:10 As the child of light walks as a child of light (v. 8b), he will continually try to discover what the will of God is so he can do it and please God.
5:11 Children of light should also abstain from joining the sons of disobedience in their deeds but should rather reprove their deeds because they are unfruitful (cf. v. 9). This is Paul's third command in this section. It is the deeds that Christians must shun, not the people who do them. We reprove these deeds as we bring the light (v. 9) next to them. This exposes them for what they are.
5:12 Believers should not even discuss the secret dark deeds of unbelievers in normal conversation. Discussing these things will just draw attention to them and may make them attractive to the carnal minded. It is better to keep what they do in the dark in the dark.
5:13 On the other hand, when light shines on evil deeds, other people see them for what they are, namely evil. This verse is not contradicting the previous one. Paul was assuring his readers that God will bring evil to the light one day and show it to be what it is. He Himself will bring all evil to the light eventually. Everything that becomes visible "is light"in the sense that it becomes obvious, not that it is good.
5:14 Since God will bring all things into the light (v. 13), it is important that believers wake up and rise from the deadness of their former unsaved lifestyles. If they do, Christ will shine on them in blessing as the sun warms what its rays touch. The source from which Paul quoted seems to have been an early Christian poem or hymn based on Isaiah 60:1.125
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