He's talking about intellectual effort, but many have found that the results of physical effort may also be futile. In this week's lesson from Luke, Jesus echoes Ecclesiastes 2:18-19 when he says "One's life does not consist in the abundance of possessions. After all, when you die, you have to leave them behind."
Allen & Williamson in their Preaching the Old Testament suggest questions we might ponder: What is the point of my life? What can we expect of life? What sense can we make of life?
The passage from Luke is a warning for us not to go after the wrong things, but Ecclesiastes says all things are futile, that nothing lasts. I'm grateful to Gene Tucker who wrote about this in Preaching Through the Christian Year C:
So what is the Christian preacher to do with this preacher's work? If this book and the Book of Job were not in our canon, the powerful but also potentially destructive wisdom doctrine that all is fair could go unchallenged. And that voice of challenge--rather than the positive and pious additions or the attribution of the work to Solomon--probably explains why this book is a part of the Jewish and Christian Scriptures. At least some of our ancestors in the faith did not cringe before Koheleth's strong words If the preacher finds it impossible to agree with Koheleth's conclusions about the futility of life, he or she can be sure that there are those in the congregation who at least now and then--if not always--experience such profound futility. Those voices deserve to be expressed and understood, even--and especially--in the context of Christian worship.