Augustine of Hippo

(Tr. xii. c. 5) As if He said, Thou understandest me to speak of a carnal birth; but a man must be born of water and of the Spirit, if he is to enter into the kingdom of God. If to obtain the temporal inheritance of his human father, a man must be born of the womb of his mother; to obtain the eternal inheritance of his heavenly Father, he must be born of the womb of the Church. And since man consists of two parts, body and soul, the mode even of this latter birth is twofold; water the visible part cleansing the body; the Spirit by His invisible cooperation, changing the invisible soul.