24 For all flesh He aptly quotes the passage from Isaiah to prove both clauses; that is, to make it evident how fading and miserable is the first birth of man, and how great is the grace of the new birth. For as the Prophet there speaks of the restoration of the Church, to prepare the way for it, he reduces men to nothing lest they should flatter themselves. I know that the words are wrongly turned by some to another sense; for some explain them of the Assyrians, as though the Prophet said, that there was no reason for the Jews to fear so much from flesh, which is like a fading flower. Others think that the vain confidence which the Jews reposed in human aids, is reproved. But the Prophet himself disproves both these views, by adding, that the people were as grass; for he expressly condemns the Jews for vanity, to whom he promised restoration in the name of the Lord. This, then, is what I have already said, that until their own emptiness has been shewn to men, they are not prepared to receive the grace of God. In short, such is the meaning of the Prophet: as exile was to the Jews like death, he promised them a new consolation, even that God would send prophets with a command of this kind. The Lord, he says, will yet say, “Comfort ye my people;” and that in the desert and the waste, the prophetic voice would yet be heard, in order that a way might be prepared for the Lord. (Isaiah 40:6.)
And as the obstinate pride which filled them, must have been necessarily purged from their minds, in order that an access might be open for God, the Prophet added what Peter relates here respecting the vanishing glory of the flesh. What is man? he says — grass; what is the glory of man? the flower of the grass. For as it was difficult to believe that man, in whom so much excellency appears, is like grass, the Prophet made a kind of concession, as though he had said, “Be it, indeed, that flesh has some glory; but lest that should dazzle your eyes, know that the flower soon withers.” He afterwards shews how suddenly everything that seems beautiful in men vanishes, even through the blowing of the Spirit of God; and by this he intimates, that man seems to be something until he comes to God, but that his whole brightness is as nothing in his presence; that, in a word, his glory is in this world, and has no place in the heavenly kingdom.
The grass withereth, or, has withered. Many think that this refers only to the outward man; but they are mistaken; for we must consider the comparison between God’s word and man. For if he meant only the body and what belongs to the present life, he ought to have said, in the second place, that the soul was far more excellent. But what he sets in opposition to the grass and its flower, is the word of God. It then follows, that in man nothing but vanity is found. Therefore, when Isaiah spoke of flesh and its glory, he meant the whole man, such as he is in himself; for what he ascribed as peculiar to God’s word, he denied to man. In short, the Prophet speaks of the same thing as Christ does in John 3:3, that man is wholly alienated from the kingdom of God, that he is nothing but an earthly, fading, and empty creature, until he is born again.