(17) Be ye not unwise.--The word here is stronger than in Ephesians 5:15; it is properly senseless, used of "the fool" (in Luke 11:40; Luke 12:20; 1Corinthians 15:36; 2Corinthians 11:16; 2Corinthians 11:19; 2Corinthians 12:6; 2Corinthians 12:11). By it St. Paul emphasises his previous warning; then he adds the explanation that to be "wise" is to "understand what the will of the Lord is"--to know His purpose towards us and towards the world, and so to know the true purpose of our life. Hence we are told in Job 28:28, that "the fear of the Lord is wisdom," or, more precisely, in Proverbs 9:10, that it is "the beginning of wisdom."

Verse 17. - Wherefore be ye not unwise, but understanding what is the will of the Lord. The "wherefore" bears on all the preceding argument: because ye are children of light; because light is so valuable and so indispensable; because your whole circumstances demand so much care and earnestness. "Unwise" is equivalent to senseless; "understanding," to both knowing and laying to heart, as in parable of sower: "When any one heareth the word of the kingdom, and understandeth it not," i.e. does not consider or ponder it, "then cometh the wicked one," etc. The will of the Lord is the great rule of the Christian life; to know and in the deeper sense understand this, is to walk wisely and to walk surely.

5:15-21 Another remedy against sin, is care, or caution, it being impossible else to maintain purity of heart and life. Time is a talent given us by God, and it is misspent and lost when not employed according to his design. If we have lost our time heretofore, we must double our diligence for the future. Of that time which thousands on a dying bed would gladly redeem at the price of the whole world, how little do men think, and to what trifles they daily sacrifice it! People are very apt to complain of bad times; it were well if that stirred them more to redeem time. Be not unwise. Ignorance of our duty, and neglect of our souls, show the greatest folly. Drunkenness is a sin that never goes alone, but carries men into other evils; it is a sin very provoking to God. The drunkard holds out to his family and to the world the sad spectacle of a sinner hardened beyond what is common, and hastening to perdition. When afflicted or weary, let us not seek to raise our spirits by strong drink, which is hateful and hurtful, and only ends in making sorrows more felt. But by fervent prayer let us seek to be filled with the Spirit, and to avoid whatever may grieve our gracious Comforter. All God's people have reason to sing for joy. Though we are not always singing, we should be always giving thanks; we should never want disposition for this duty, as we never want matter for it, through the whole course of our lives. Always, even in trials and afflictions, and for all things; being satisfied of their loving intent, and good tendency. God keeps believers from sinning against him, and engages them to submit one to another in all he has commanded, to promote his glory, and to fulfil their duties to each other.Wherefore be ye not unwise,.... No one would be thought to be unwise, but such are, who do not redeem time, and are ignorant of the will of the Lord; believers should not act the unwise part, neither in their talk, nor in their walk and conversation, nor in their use of time:

but understanding what the will of the Lord is; or "of God", as read the Alexandrian copy, the Vulgate Latin, Syriac, and Ethiopic versions: there is the secret will of God, which is the rule of all his proceedings; and is unknown to men, till facts make it appear; this is always fulfilled, and sometimes by persons who have no regard to his revealed will; to this the wills of the people of God should be always resigned: and there is his revealed will, which lies partly in the Gospel; which declares it to be his will, that Christ should work out the salvation of his people, which is what he came to do; that whoever believes in him shall be saved; that all that are redeemed shall be sanctified; and that they shall persevere to the end, and be glorified; and partly in the law, in the precepts and commands of it, which contain the good, perfect, and acceptable will of God: and the understanding of it is not a mere speculative knowledge of it, but a practical one; when a man not only knows, but does the will of God, and his heart and actions agree with it; and this is to be done in faith, in virtue of grace and strength received, with a view to the glory of God, having no dependence on what is done; and to the right understanding of it, so as to act according to it, as should be, the word of God, and the illuminations, instructions, and grace of the Spirit, are necessary: the Alexandrian copy, Syriac, Arabic, and Ethiopic versions, read the words as an exhortation, "understand ye the will of God".