For to all who know the Gospel it is apparent that by the Lord’s voice the care of the whole Church was committed to the holy Apostle and Prince of all the Apostles, Peter. For to him it is said, Peter, do you love Me? Feed My sheep John 21:17. To him it is said, Behold Satan has desired to sift you as wheat; and I have prayed for you, Peter, that your faith fail not. And thou, when you are converted, strengthen your brethren Luke 22:31. To him it is said, You are Peter, and upon this rock I will build My Church, and the gates of hell shall not prevail against it. And I will give unto you the keys of the kingdom of heaven and whatsoever you shall bind an earth shall be bound also in heaven; and whatsoever you shall loose on earth shall be loosed also in heaven Matthew 16:18.
Lo, he received the keys of the heavenly kingdom, and power to bind and loose is given him, the care and principality of the whole Church is committed to him, and yet he is not called the universal apostle; while the most holy man, my fellow priest John, attempts to be called universal bishop. I am compelled to cry out and say, O tempora, O mores!
CHURCH FATHERS: Registrum Epistolarum, Book V, Letter 20 (Gregory the Great)