For, as regards his proper personality, he was by nature one man, by grace one Christian, by still more abounding grace one, and yet also, the first apostle; but when it was said to him, "I will give unto thee the keys of the kingdom of heaven, and whatsoever thou shalt bind on earth, shall be bound in heaven; and whatsoever thou shalt loose on earth, shall be loosed in heaven," he represented the universal Church, which in this world is shaken by divers temptations, that come upon it like torrents of rain, floods and tempests, and falleth not, because it is founded upon a rock (petra), from which Peter received his name.
For petra (rock) is not derived from Peter, but Peter from petra; just as Christ is not called so from the Christian, but the Christian from Christ. For on this very account the Lord said, "On this rock will I build my Church," because Peter had said, "Thou art the Christ, the Son of the living God." On this rock, therefore, He said, which thou hast confessed. I will build my Church.
For the Rock (Petra) was Christ; and on this foundation was Peter himself also built.