Theophylact of Ohrid

The Apostle showed the superiority of spiritual rebirth over fleshly birth, and pointed out the worthlessness of mortal glory, namely, that birth is joined with corruption and impurity, and glory differs in nothing from spring plants, whereas the word of the Lord experiences nothing of the sort. For every human opinion quickly ceases, but the word of God is not so — it has eternal abiding. With this purpose he added: "that word which was preached to you."

Commentary on 1 Peter ↗

Clement of Alexandria

"Being born again, not of corruptible seed." The soul, then, which is produced along with the body is corruptible, as some think.

From the Latin Translation of Cassiodorus ↗

Bede

Born not of corruptible seed, etc. Such is in the Gospel of John: To those who believed in his name, who were born not of blood, nor of the will of the flesh, nor of the will of man, but of God (John 1). Therefore, just as the price of the Lord's passion by which we have been redeemed is incorruptible, so also is the sacrament of the holy font by which we are reborn. These are so interconnected with each other that neither can confer salvation upon us without the other. …

Commentary on the Catholic Epistles ↗