For who knoweth what is {a} good for man in this life, all the days of his vain life which he spendeth as a shadow? for who can tell a man what shall be after him under the sun?

(a) There is no state in which man can live to have perfect quietness in this life.

Wesley's Notes

6:12 Who knoweth - No man certainly knows what is better for him here, whether to be high or low, rich or poor. Vain life - Life itself is a vain and uncertain thing, and therefore all things which depend on it must be so too. While - While it abides, hath nothing solid, or substantial in it, and which speedily passes away, and leaves no sign behind it. For - And as no man can be happy with these things while he lives, so he can have no content in leaving them to others, because he knows not either who shall possess them, or how the future owners will use or abuse them.

King James Translators' Notes

all...: Heb. the number of the days of the life of his vanity

Jamieson-Fausset-Brown Bible Commentary

12. For who knoweth, &c.-The ungodly know not what is really "good" during life, nor "what shall be after them," that is, what will be the event of their undertakings (Ec 3:22; 8:7). The godly might be tempted to "contend with God" (Ec 6:10) as to His dispensations; but they cannot fully know the wise purposes served by them now and hereafter. Their sufferings from the oppressors are more really good for them than cloudless prosperity; sinners are being allowed to fill up their measure of guilt. Retribution in part vindicates God's ways even now. The judgment shall make all clear. In Ec 7:1-29, he states what is good, in answer to this verse.

Matthew Henry's Concise Commentary

6:7-12 A little will serve to sustain us comfortably, and a great deal can do no more. The desires of the soul find nothing in the wealth of the world to give satisfaction. The poor man has comfort as well as the richest, and is under no real disadvantage. We cannot say, Better is the sight of the eyes than the resting of the soul in God; for it is better to live by faith in things to come, than to live by sense, which dwells only upon present things. Our lot is appointed. We have what pleases God, and let that please us. The greatest possessions and honours cannot set us above the common events of human life. Seeing that the things men pursue on earth increase vanities, what is man the better for his worldly devices? Our life upon earth is to be reckoned by days. It is fleeting and uncertain, and with little in it to be fond of, or to be depended on. Let us return to God, trust in his mercy through Jesus Christ, and submit to his will. Then soon shall we glide through this vexatious world, and find ourselves in that happy place, where there is fulness of joy and pleasures for evermore.

Matthew Henry's Whole Bible Commentary

Verses 11-12

Here, 1. Solomon lays down his conclusion which he had undertaken to prove, as that which was fully confirmed by the foregoing discourse: There be many things that increase vanity; the life of man is vain, at the best, and there are abundance of accidents that concur to make it more so; even that which pretends to increase the vanity and make it more vexatious. 2. He draws some inferences from it, which serve further to evince the truth of it. (1.) That a man is never the nearer to true happiness for the abundance that he has in this world: What is man the better for his wealth and pleasure, his honour and preferment? What remains to man? What residuum has he, what overplus, what real advantage, when he comes to balance his accounts? Nothing that will do him any good or turn to account. (2.) That we do not know what to wish for, because that which we promise ourselves most satisfaction in often proves most vexatious to us: Who knows what is good for a man in this life, where every thing is vanity, and any thing, even that which we most covet, may prove a calamity to us? Thoughtful people are in care to do every thing for the best, if they knew it; but as it is an instance of the corruption of our hearts that we are apt to desire that as good for us which is really hurtful, as children that cry for knives to cut their fingers with, so is it an instance of the vanity of this world that what, according to all probable conjectures, seems to be for the best, often proves otherwise; such is our shortsightedness concerning the issues and events of things, and such broken reeds are all our creature-confidences. We know not how to advise others for the best, nor how to act ourselves, because that which we apprehend likely to be for our welfare may become a trap. (3.) That therefore our life upon earth is what we have no reason to take any great complacency in, or to be confident of the continuance of. It is to be reckoned by days; it is but a vain life, and we spend it as a shadow, so little is there in it substantial, so fleeting, so uncertain, so transitory is it, and so little in it to be fond of or to be depended on. If all the comforts of life be vanity, life itself can have no great reality in it to constitute a happiness for us. (4.) That our expectations from this world are as uncertain and deceitful as our enjoyments are. Since every thing is vanity, Who can tell a man what shall be after him under the sun? He can no more please himself with the hopes of what shall be after him, to his children and family, than with the relish of what is with him, since he can neither foresee himself, nor can any one else foretel to him, what shall be after him. Nor shall he have any intelligence sent him of it when he is gone. His sons come to honour, and he knows it not. So that, look which way we will, Vanity of vanity, all is vanity.