“So then do not be foolish, but understand what the will of the Lord is.” Ephesians 5:17
“You were formally in darkness” is preceded by the command “walk as children of light” (Eph. 5:8). This title, children of light, is used only three other times in the New Testament once by the Lord Jesus to contrast worldly wisdom with the ineffectual use of godly wisdom in the least things (Luke 16:8); once again to direct us direct us to believe in the light (John 12:36); and finally by Paul to encourage us to be alert and be sober (1 Thess. 5:5-6).
A light-like life, which is evidence of the fruit of the Spirit, is expressed in the character of goodness (Rom. 15:14), righteousness (Rom. 14:17-18), and truth (Eph. 5:9; compare Gal. 5:22). In fact, the transformation of our character by our conscious choice “to present your bodies a living and holy sacrifice, acceptable to God” enables us to “prove what the will of God is, that which is good and acceptable and perfect” (Rom. 12:1-2; see also Eph. 5:10). An equation is clearly drawn between godly behavior and godly wisdom.
It therefore follows that children of light “do not participate in the unfruitful deeds of darkness” (Eph. 5:11), taking the responsibility to reprove them and recognizing “it is disgraceful even to speak of the things which are done by them in secret” (Eph. 5:12).
The light things make manifest (present, display) that which is reproved, “Therefore be careful how you walk, not as unwise men but as wise” (Eph. 5:15). That wisdom is not the foolish wisdom of this world (1 Cor. 1:20), but the wisdom of God (1 Cor. 2:7) “so that we may know the things freely given to us by God” (1 Cor. 2:12), understanding what the will of the Lord is.