God knows the frailty of every man, “He is mindful that we are but dust” (Psa 103:14). David courageously asked the Lord, “make me to know my end and what is the extent of my days; let me know how transient I am. Behold, You have made my days as handbreadths, and my lifetime as nothing in Your sight; surely every man at his best is a mere breath” (Psa 39:4-5). Job perceived the brevity of his life and declared, “I will not live forever…for my days are but a breath” (Job 7:16), and James wrote, “you are just a vapor that appears for a little while and then vanishes away” (Jam 4:14b).
It is often true that when we’re young we do not think about the brevity of life, but as time advances we’re prone to reflect on such matters. Wisdom calls us to live with a mind set on eternity, for at any moment God may pluck us from this world and bring us into His presence. Before we were born, God determined all the days of our lives, as Scripture reveals, “in Your book were all written the days that were ordained for me, when as yet there was not one of them” (Psa 139:16).
It’s a sign of spiritual maturity when a believer lives in the reality of his own mortality and adopts a biblical perspective on God and eternity. Such a believer does not concern himself with the daily affairs of this world, except how he might please the Lord and show love to others (2 Cor 5:9; 1 Th 4:9). The growing Christian realizes there is no eternal value in the accumulation of wealth, nice homes or expensive cars, as these are only fuel for the great fire (2 Pet 3:10-12; Rev 21:1). This does not mean the believer cannot enjoy wealth if God gives it; certainly he can (Eccl 3:12-13; 5:19-20; 9:9). Rather, the mature believer does not hold tightly to material things, but walks in the truth that one life will soon be past, and only what’s done for Christ will last. It is on God and heaven that the believer must focus his thoughts and energy, for “he who confesses that there is nothing solid or stable on the earth, and yet firmly retains his hope in God, undoubtedly contemplates a happiness reserved for him elsewhere.”
The Vanity of Man as Mortal
Teach me the measure of my days,
Thou Maker of my frame;
I would survey life’s narrow space,
And learn how frail I am.
A span is all that we can boast,
An inch or two of time;
Man is but vanity and dust
In all his flower and prime.
See the vain race of mortals move
Like shadows o’er the plain;
They rage and strive, desire and love,
But all the noise is vain.
Some walk in honor’s gaudy show,
Some dig for golden ore;
They toil for heirs, they know not who,
And straight are seen no more.
What should I wish or wait for, then,
From creatures earth and dust?
They make our expectations vain,
And disappoint our trust.
Now I forbid my carnal hope,
My fond desires recall;
I give my mortal interest up,
And make my God my all.
Dr. Steven R. Cook
 John Calvin, Institutes of the Christian Religion, II (Bellingham, WA: Logos Bible Software, 1997) chapter x, section 15.