Psalms 90:5

In the morning let it pass like grass, in the morning let it flower and pass away: in the evening let it fall, harden, and wither. O the mysteries of the Scriptures! In the morning let it pass like grass. Our Lord and Savior also speaks in the Gospel about the hay, which springs up in one day and withers in one day. Just as grass that is green and flowers seems in the morning to be, as it were, a flower and green: yet when the sun comes and scorches it, toward evening it wilts, as it were, and falls; so too all our life seems to be, as it were, a flower while it is green, and it withers. Ten years ago you saw a young lad: nothing more beautiful than he, he ran this way and that. If you look at him now, he seems in old age to be, as it were, dead. Though he lives in old age, yet his youth has perished. In the morning let it pass like grass, that is, our youth: for that is the morning. Let it pass like grass, in the morning let it flower and pass away. We flower in youth, we wither in old age. In the evening let it fall, harden, and wither.

Next, the man of God, or rather the Prophetic spirit, seems to be reciting some law written in the secret wisdom of God, in which He has fixed a limit to the sinful life of mortals, and determined the troubles of mortality, in the following words: "Their years are as things which are nothing worth: in the morning let it fade away like the grass" [Psalm 90:5]. The happiness therefore of the heirs of the old covenant, which they asked of the Lord their God as a great boon, attained to receive this Law in His mysterious Providence. Moses seems to be reciting it: "Their years shall be things which are esteemed as nothing." Such are those things which are not before they are come: and when come, shall soon not be: for they do not come to be here, but to be gone. "In the morning," that is, before they come, "as a heat let it pass by;" but "in the evening," it means after they come, "let it fall, and be dried up, and withered" [Psalm 90:6]. It is "to fall" in death, be "dried up" in the corpse, "withered" in the dust. What is this but flesh, wherein is the accursed lust of fleshly things? "For all flesh is grass, and all the goodliness of man as the flower of the field; the grass withereth, the flower fadeth: but the word of the Lord abideth for ever."

Their years shall be counted as nothing. What he says is this: since man from the beginning of the world lived nearly a thousand years, and a thousand years before God are as a watch in the night. Nay, I have said enough: the ages of men are as nothing in comparison with the divine eternity. Do you wish to know more fully how human life is nothing? Hear what follows. In the morning let it pass like grass. As the morning dew passes swiftly, so is the life of men. Our morning is youth. In the morning let it flower and pass. In youth and full age we flowered, but in old age we fall down, and the flower of our strength has withered. For which of us knows how our age passes by? While we scarcely know it, old age steals up on us from behind. In the evening let it fall, harden, and grow dry. Our evening is old age, which, when the flower of youth has been shaken off, is hardened by the manifold horror of diseases. "For all flesh indeed is grass, and its glory is as the flower of grass: it withered and fell; but the word of the Lord abides forever." We still live, and part of us has already perished in old age: though the mind is the same, yet we who feel that we have lost the vigor of our former youth are in a manner become other men.