See then. If believers must not neglect to drive away the darkness of others by their own brightness, how much less ought they to be blind as to their own conduct in life? What darkness shall conceal those on whom Christ, the Sun of righteousness, has arisen? Placed, as it were, in a crowded theater, they ought to live under the eye of God and of angels. Let them stand in awe of these witnesses, though they may be concealed from the view of all mortals. Dismissing the metaphor of darkness and light, he enjoins them to regulate their life circumspectly as wise men, [1] who have been educated by the Lord in the school of true wisdom. Our understanding must shew itself by taking God for our guide and instructor, to teach us his own will.

Footnotes

1 - "In me hos asophoi all ' hos sophoi we have an antithetical parallelism, (such as is found in the Classical as well as the Scriptural writers,) where, for emphasis' sake, a proposition is expressed both affirmatively and negatively, as in John 1:20, homologese kai ouk ernesato, he confessed and denied not.' By asophoi, and sophoi are meant the persons just before denoted by kotos and phos, and, a little after, termed aphrones and sunientes, by a frequent Hebrew idiom, whereby Wisdom stands for Virtue, and Folly for Vice" -- Bloomfield.

See then that ye walk circumspectly - carefully, anxiously, solicitous lest you fall into sin. The word rendered "circumspectly" - ἀκριβῶς akribōs - means "diligently," and the idea here is, that they were to take special pains to guard against the temptations around them, and to live as they ought to.
Not as fools, but as wise - Not as the people of this world live, indulging in foolish pleasures and desires, but as those who have been taught to understand heavenly wisdom, and who have been made truly wise.

Walk circumspectly - Our word circumspect, from the Latin circirmspicio, signifies to look round about on all hands; to be every way watchful, wary, and cautious, in order to avoid danger, discern enemies before they come too nigh, and secure a man's interest by every possible and lawful means. But the original word ακριβως signifies correctly, accurately, consistently, or perfectly. Be ye, who have received the truth, careful of your conduct; walk by the rule which God has given you; do this as well in little as in great matters; exemplify your principles, which are holy and good, by a corresponding conduct; do not only profess, but live the Gospel. As you embrace all its promises, be careful also to embrace all its precepts; and behave yourselves so, that your enemies may never be able to say that ye are holy in your doctrines and profession, but irregular in your lives.
Not as fools, but as wise - Μη ὡς ασοφοι, αλλ' ὡς σοφοι. The heathens affected to be called σοφοι, or wise men. Pythagoras was perhaps the first who corrected this vanity, by assuming the title of φιλοσοφος, a lover of wisdom; hence our term philosopher, used now in a much prouder sense than that in which the great Pythagoras wished it to be applied. The apostle here takes the term σοφος, and applies it to the Christian; and, instead of it, gives the empty Gentile philosopher the title of ασοφος, without wisdom, fool.

(4) See then that ye walk circumspectly, not as fools, but as wise,
(4) The worse and more corrupt that the manners of this world are, the more watchful we ought to be in every situation, and give regard to nothing but the will of God.

See then that ye walk circumspectly,.... The Alexandrian copy and the Vulgate Latin version read, "see then, brethren", it being an exhortation to the saints at Ephesus, upon the foregoing discourse and citation, to take heed to their walk: the believer's walk is both inward and outward; his inward walk is by faith on Christ; his outward walk is his conversation among men: this supposes life; requires strength and prudence; denotes continuance and progression; with patience and courage: this walk should be seen to, and watched over; a man should see to it that he does walk, and to the way in which he walks, and how he walks; that he walks circumspectly, with his eyes about him; that he walks with diligence, caution, accuracy, and exactness, to the uttermost of his strength and power; and with wisdom and prudence, looking well to his going:
not as fools, but as wise; such walk like fools, whose eyes are not upon their ways; who walk in their own ways, which are crooked, and ways of darkness, and lead to destruction; who walk after the flesh, and naked, without the garments of a holy life and conversation; and with lamps, but no oil in them: and such walk as wise men, who walk according to the rule of God's word, make Christ their pattern, have the Spirit for their guide, and walk as becomes the Gospel of Christ; inoffensively to all men, in wisdom towards them that are without, and in love to them that are within; and as pilgrims and strangers in this world, looking for a better country; and so as to promote the glory of God, and the good of souls.

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.

that--rather as Greek, "See how ye walk," &c. The double idea is compressed into one sentence: "See (take heed) how ye walk," and "See that ye walk circumspectly." The manner, as well as the act itself, is included. See how ye are walking, with a view to your being circumspect (literally, accurate, exact) in your walk. Compare Colossians 4:5, "Walk in wisdom (answering to 'as wise' here) toward them that are without" (answering to "circumspectly," that is, correctly, in relation to the unbelievers around, not giving occasion of stumbling to any, but edifying all by a consistent walk).
not as fools--Greek, "not as unwise, but as wise."

Walk circumspectly. The Revision makes the meaning clear.
Redeeming the time. Using every opportunity; buying them by giving up present enjoyment.
Be ye not unwise. That is, so foolish as to not understand the will of the Lord.

Circumspectly - Exactly, with the utmost accuracy, getting to the highest pitch of every point of holiness. Not as fools - Who think not where they are going, or do not make the best of their way.