Commentaries:
In chapter 2, Solomon launches into what he had learned about his works of building material things like houses and gardens and seeking even greater wealth. His conclusion? All of these material achievements were nothing but vanity, a grasping after wind.
He finds no real, sustained profit in them, nothing that truly added to his quality of life, no lasting fulfillment. He does not mean they resulted in no sense of achievement or passing pleasure, but that their fruit never truly fulfilled God's purpose for man. Therefore, those things are poor substitutes for a sustained sense of well-being. He then proceeds into an exploration of wine and entertainment. These are simply another form of materialism, ways of pleasing the flesh. He concludes that they, too, are folly, a mad pursuit.
John W. Ritenbaugh
Ecclesiastes and Christian Living (Part Seven): Contentment
Solomon is forced to ask himself, "What can the person who follows Solomon do that Solomon has not already done? He did it better than his successor can ever hope to do, because God had endowed him with so many gifts. His conclusion: His successor will be able to do only what he has already done.
Wisdom does have goodness to it; it is not without value. It is certainly far better than foolishness, but it is not the ultimate source of reliance. One cannot put his trust in his worldly wisdom.
John W. Ritenbaugh
Ecclesiastes and the Feast of Tabernacles (Part 2)