The Pope is the Supreme Pontiff of Rome, the Vicar of Christ on the earth, whom we are obligated to obey.
Jesus Christ is the good Shepherd, Who gave His life on a cross for his sheep; He is the Shepherd of our souls, Who bought them with the price of His blood: but this divine Shepherd, having fulfilled the work of our redemption, had to absent Himself from the earth and return to heaven from which He had come; and in order not to leave his beloved flock without a visible Shepherd to guide it among the infinite dangers and deviations from this world to the kingdom of heaven, he chose Saint Peter from the Apostles and he entrusted him with the discharging of this glorious and supreme duty.
The third time that Jesus Christ appeared to His Apostles and disciples after His Resurrection, addressing Saint Peter He asked these questions. "Simon, son of John (Saint Peter was called thus), dost thou love me [agapas me] more than these do?" He said to Him, "Yes, Lord, thou knowest that I love thee [philo se]." He said to him, "Feed my lambs." He said to him a second time, "Simon, son of John, dost thou love me [agapas me]?" He said to him, "Yes Lord thou knowest that I love thee [philo se]." He said to him, "Feed my lambs." A third time he said to him, "Simon, son of John, dost thou love me [phileis me]?" Peter was grieved because he said to him for the third time, "Dost thou love me [phileis me]?" And he said to him, "Lord, thou knowest all things, thou knowest that I love thee [philo se]." He said to him, "Feed my sheep." (John 21:15-17) With these words, so brief and loving as they are full of power and authority, he entrusts to Saint Peter and to all his legitimate Successors, not only the faithful, signified by the lambs, but also the Shepherds represented by the sheep. He made him the Apostle of the Apostles, the Bishop of the Bishops, the Prince of the Princes of the Church, and the universal Shepherd of the entire flock and of the Pastors of the flock.
Finally, He declared him, not His successor, because no one could be that of Jesus Christ, but rather His Vicar and visible Head of the Church, of Whom Jesus Christ Himself is the invisible head. And since the Church must exist until the end of the ages, according to His divine promise, and be always visible, Her visible head should also exist until then, not in the person of Saint Peter, being mortal, who paid his tribute to death in Rome many centuries ago, but rather in his legitimate Successors, who are the Bishops of Rome, whom we call Popes, which means Fathers, because so they are of all christians, whom all christians are obliged to obey.
El Catecismo de la Doctrina Cristiana, Mazo, p. 80-81 (Plinthos' translation)