Psalm 39:5

Behold, thou hast made my days [as] an handbreadth
These words, with the following clause, are the psalmist's answer to his own inquiries; or rather a correction of his inquiry and impatience, showing how needless it was to ask such questions, and be impatient to die, when it was so clear and certain a case that life was so short; not a yard or ell (forty five inches), but an handbreadth, the breadth of four fingers; or at most a span of time was allowed to man, whose days are few, like the shadow that declineth, and the grass that withers; by which figurative expressions the brevity of human life is described, ( Psalms 102:11 ) ( 103:15 ) ; and this is the measure made, cut out, and appointed by the Lord himself, who has determined the years, months, and days of man's life, ( Job 14:5 ) ;

and mine age [is] as nothing before thee;
in the sight of God, or in comparison of his eternity; not so much as an handbreadth, or to be accounted as an inch, but nothing at, all; yea, less than nothing, and vanity; see ( Isaiah 40:17 ) ; that is, the age or life of man in this world, as the word ^F23 used signifies; for otherwise the age or life of man, in the world to come, is of an everlasting duration; but the years of this present life are threescore and ten; ordinarily speaking; an hundred and thirty are by Jacob reckoned but few; and even a thousand years with the Lord are but as one day, ( Psalms 90:4 Psalms 90:10 ) ;

verily every man at his best state is altogether vanity.
As vanity may signify sin, emptiness, folly, falsehood, fickleness, and inconstancy; for man is a very sinful creature, empty of all that is good; foolish as to the knowledge of divine things; he is deceiving and deceived, his heart is deceitful and desperately wicked; and he is unstable in all his ways: he is "all vanity" ^F24, as the words may be rendered; all that he has, or is, or is in him, is vanity; his body, in the health, beauty, and strength of it, is subject to change; and so are his mind, his memory, his judgment and affections, his purposes and promises; and so are his goods and estate, his riches and honours; yea, all the vanity that is in the creatures, that is, in the vegetable and sensitive creatures, yea, that is in the whole, world, is in him; who is a microcosm, a little world himself: and this is true of every man, even in his "best settled" ^F25 estate; when he stood the most firm, as the word used signifies; it is true of men of high and low degree, of the wise, knowing, and learned, as well as of the illiterate and ignorant, ( Psalms 62:9 ) ( Romans 1:21 Romans 1:22 ) ; even of those that are in the most prosperous circumstances, in the greatest ease and affluence, ( Luke 12:16-19 ) ; David himself had an experience of it, ( 2 Samuel 7:1 ) ( 12:11 ) ; yea, this is true of Adam in his best estate, in his estate of innocence; for he was even then subject to change, as the event has shown; and being in honour, he abode not long; and, though upright, became sinful, and came short of the glory of God: indeed, the spiritual estate of believers in Christ is so well settled as that it cannot be altered; nor is it subject to any vanity.

Selah. (See Gill on Psalms 3:2).