And Jesus answering said to him: "And I say to thee: That thou art Peter; and upon this rock I will build my church, and the gates of hell shall not prevail against it. And I will give to thee the keys of the kingdom of heaven. And whatsoever thou shalt bind upon earth, it shall be bound also in heaven: and whatsoever thou shalt loose on earth, it shall be loosed also in heaven." (Matt. 16:18-19)
THE POPE: St. Peter became the first Bishop of Rome, and for that reason the Roman Bishop has ever been believed to be the successor of St. Peter in the Primacy. Hence he is called the 'Pope,' i. e. the father of all the faithful. The Papacy therefore is of divine institution.
[From 'A Practical Commentary on Holy Scripture' by Bishop Knecht, D.D.]
(1899 Douay-Rheims Bible)