Psalm 39.5And while Psalm 90 doesn't mention hebel, it is very much a description of hebel and suggests that a proper understanding of hebel creates a "heart of wisdom":
You have made my days a mere handbreadth;
the span of my years is as nothing before you.
Everyone is but a breath [hebel],
even those who seem secure.
Psalm 114.3-4
Lord, what are human beings that you care for them,
mere mortals that you think of them?
They are like a breath [hebel];
their days are like a fleeting shadow.
Psalm 90.3-6, 10, 12Life is hebel, our years "quickly pass, and then we fly away." So the encouragement in Psalm 90 is, in my estimation, the same encouragement in Ecclesiastes: "Teach us to number our days that we may gain a heart of wisdom."
You turn people back to dust,
saying, “Return to dust, you mortals.”
A thousand years in your sight
are like a day that has just gone by,
or like a watch in the night.
Yet you sweep people away in the sleep of death—
they are like the new grass of the morning:
In the morning it springs up new,
but by evening it is dry and withered.
Our days may come to seventy years,
or eighty, if our strength endures;
yet the best of them are but trouble and sorrow,
for they quickly pass, and we fly away.
Teach us to number our days,
that we may gain a heart of wisdom.
In light of this, what about the great theme of vanity in the book of Ecclesiastes?
Again, I'd argue that hebel itself isn't "vanity" or "meaninglessness," those translations are second-order value judgments that reflect how hebel, given its transient nature, can create futility in human striving. This is less a commentary about the intrinsic nature of hebel than how we attempt to grasp at hebel, the "chasing after the wind" mentioned repeatedly in Ecclesiastes. What is vain is this grasping and chasing after hebel. It's the interaction of the two--hebel plus grasping--that creates the futility.
So what are we chasing? What are we grasping at?
A clue comes right at the start of the book, in 1.3:
What do people gain from all their labors at which they toil under the sun?The word translated as "gain" here is yithron. Yithron only occurs ten times in the OT, and all of those occurrences are in the book of Ecclesiastes.
Yithron is variously translated as "gain," "profit," or "advantage." The basic idea is that of accumulation, excess, and remainder--what is "left over." Basically, to use a financial metaphor, yithron is getting life "into the black" as it were.
Obviously, because life is hebel, efforts to "gain" are futile and vain. Thus the examples given in the first part of Ecclesiastes about how all sorts of efforts at gaining or acquiring--creating an "excess"--are futile. Death washes any sort of "profit"--the excess remainder of your life--away.
This acquisitive grasping--this chasing after the wind--is what is vain. It's the combination of hebel and yithron that makes for the vanity. Crudely:
hebel + yithron = vanityI highlight this interaction between hebel and yithron as, again, I don't think the fleeting nature of life is intrinsically meaningless or vain. Rather, it is how we stand in relation to hebel that creates the problems. The problem, to create a neologism, is a yithronic posture toward hebel--a grasping, profiting, acquiring, acquisitive, chasing attitude given life's fleeting, vaporous, misty, impermanent, and transitory nature.
wind + chasing = vanity