““O Lord, make me know my end and what is the measure of my days; let me know how fleeting I am! Behold, you have made my days a few handbreadths, and my lifetime is as nothing before you. Surely all mankind stands as a mere breath! Selah Surely a man goes about as a shadow! Surely for nothing they are in turmoil; man heaps up wealth and does not know who will gather!” -Psalm 39:4–6
The Psalmist moves from acknowledging the difficulty of his situation, that is his ability to remain quiet in the face of suffering, to seeking understanding: “Make me know my end and what is the measure of my days;”
Perhaps his physical frailty has raised awareness of his own mortality because there is a stark awareness of it here. He sees his existence as “fleeting,” “a few handbreadths,” “nothing before God,” and “mere breath.”
There are echoes of Job’s lament in his prayer: ““Remember that my life is a breath; my eye will never again see good.” -Job 7:7
And also of Moses whose song is recorded in Psalm 90: “in the morning it flourishes and is renewed; in the evening it fades and withers. For we are brought to an end by your anger; by your wrath we are dismayed. You have set our iniquities before you, our secret sins in the light of your presence. For all our days pass away under your wrath; we bring our years to an end like a sigh. The years of our life are seventy, or even by reason of strength eighty; yet their span is but toil and trouble; they are soon gone, and we fly away. Who considers the power of your anger, and your wrath according to the fear of you? So teach us to number our days that we may get a heart of wisdom.” -Psalm 90:6–12
James acknowledges this brevity of life as well: “yet you do not know what tomorrow will bring. What is your life? For you are a mist that appears for a little time and then vanishes.” -James 4:14
And what is the conclusion of this matter? That man tends to run about full of hurry, scurry, fret, and worry—and for what? For no good reason. Because man—and as the Psalmist is discovering of himself—has missed the point of his existence. For all that he accumulates in this life will be spent by someone else. This is a lesson Solomon—if he is the author of Ecclesiastes—has also learned well.
“I hated all my toil in which I toil under the sun, seeing that I must leave it to the man who will come after me, and who knows whether he will be wise or a fool? Yet he will be master of all for which I toiled and used my wisdom under the sun. This also is vanity. So I turned about and gave my heart up to despair over all the toil of my labors under the sun, because sometimes a person who has toiled with wisdom and knowledge and skill must leave everything to be enjoyed by someone who did not toil for it. This also is vanity and a great evil.” -Ecclesiastes 2:18–21
To this end, the first question of The Westminster Shorter Catechism asks: What is the Chief End of Man? The answer can be found here.