As for man - literally, "Man; like the grass are his days!" The thought is fixed on man: man so frail and weak; man, not only made originally of earth, but man delicate, feeble, soon to pass away like the springing grass, or like the fading flower.
His days are as grass - See the notes at Psalm 90:5-6; compare Isaiah 40:6-8, notes; 1-Peter 1:24, note.
As a flower of the field - As a blossom. It opens with beauty and fragrance, but soon fades and perishes.
So he flourisheth - Rather, "So he blossoms." That is, he is like a flower that is fresh and beautiful, and that soon withers away.

His days are as grass - See the note on Psalm 90:5.

[As for] (i) man, his days [are] as grass: as a flower of the field, so he flourisheth.
(i) He declares that man has nothing in himself to move God to mercy, but only the confession of his infirmity and misery.

As for man, his days are as grass,.... He himself is like the grass which springs out of the earth; continues on it for a time, and then drops into it; the continuance of the grass is very short, it flourishes in the morning, is cut down at evening, and withers; see Psalm 90:5. As a flower of the field, so he flourisheth; which denotes the goodliness of man, and describes him in his best estate, as possessed of health, riches, honour, and all the gifts and endowments of nature; and yet, with all these, is only like a field flower, exposed to every wind, liable to be cropped by every hand, and to be trampled upon by the beasts of the field; and therefore flourishes not long: so very precarious and uncertain is man in his most flourishing circumstances; see Isaiah 40:6.

How short is man's life, and uncertain! The flower of the garden is commonly more choice, and will last the longer, for being sheltered by the garden-wall, and the gardener's care; but the flower of the field, to which life is here compared, is not only withering in itself, but exposed to the cold blasts, and liable to be cropped and trod on by the beasts of the field. Such is man. God considers this, and pities him; let him consider it himself. God's mercy is better than life, for it will outlive it. His righteousness, the truth of his promise, shall be unto children's children, who tread in the footsteps of their forefathers' piety. Then shall mercy be preserved to them.

So short and frail is life that a breath may destroy it.
it is gone--literally, "it is not."
know it no more--no more recognize him (Psalm 90:6; Isaiah 40:6-8).

The figure of the grass recalls Psalm 90:5., cf. Isaiah 40:6-8; Isaiah 51:12; that of the flower, Job 14:2. אנושׁ is man as a mortal being; his life's duration is likened to that of a blade of grass, and his beauty and glory to a flower of the field, whose fullest bloom is also the beginning of its fading. In Psalm 103:16 בּו (the same as in Isaiah 40:7.) refers to man, who is compared to grass and flowers. כּי is ἐάν with a hypothetical perfect; and the wind that scorches up the plants, referred to man, is an emblem of every form of peril that threatens life: often enough it is really a breath of wind which snaps off a man's life. The bold designation of vanishing away without leaving any trace, "and his place knoweth him no more," is taken from Job 7:10, cf. ibid. Job 8:18; Job 20:9. In the midst of this plant-like, frail destiny, there is, however, one strong ground of comfort. There is an everlasting power, which raises all those who link themselves with it above the transitoriness involved in nature's laws, and makes them eternal like itself. This power is the mercy of God, which spans itself above (על) all those who fear Him like an eternal heaven. This is God's righteousness, which rewards faithful adherence to His covenant and conscientious fulfilment of His precepts in accordance with the order of redemption, and shows itself even to (ל) children's children, according to Exodus 20:6; Exodus 34:7; Deuteronomy 7:9 : on into a thousand generations, i.e., into infinity.