57. Moreover, that thou mayest know that it is after His Manhood that He entreats, and in virtue of His Godhead that He commands, it is written for thee in the Gospel that He said to Peter: “I have prayed for thee, that thy faith fail not.” To the same Apostle, again, when on a former occasion he said, “Thou art the Christ, the Son of the living God,” He made answer: “Thou art Peter, and upon this Rock will I build My Church, and I will give thee the keys of the kingdom of heaven.” Could He not, then, strengthen the faith of the man to whom, acting on His own authority, He gave the kingdom, whom He called the Rock, thereby declaring him to be the foundation of the Church? Consider, then, the manner of His entreaty, the occasions of His commanding. He entreats, when He is shown to us as on the eve of suffering: He commands, when He is believed to be the Son of God.