christ establishes the hierarchy:

After his resurrection, but before ascending to his Father in heaven, Christ set about establishing good order in the Church he was building up on earth. Before the passion, Christ told his apostle Peter that the Church would be built on the rock of his faith. “I tell you, you are Peter, and on this rock I will build my Church, and the gates of Hades shall not prevail against it. I will give you the keys of the kingdom of heaven, and whatever you bind on earth shall be bound in heaven” (Matthew 16:18-19). Since Peter denied Christ three times during the passion, Christ was sure to reinstate him three times, canceling his wicked denial (John 21:15-19). The successors of all the apostles the Church now calls bishops. The successor of St. Peter is called the Supreme Pontiff, or, the Pope (CCC 882, 883).

After Pentecost, Peter and the apostles led the Church with the authority given to them by Christ. When controversies arose among the faithful, the apostles gathered together in council to discuss the matter. After the debate, Peter arose and announced the judgment of the Church (Acts 15). This model holds in the Church to this day. When all the bishops of the Church gather together to settle questions of faith and morals, this is called an ecumenical council (CCC 884). There have been twenty-one ecumenical councils since the one described in the Book of Acts, beginning with Nicea I in 325 and ending with Vatican II in 1965. Just as the Church is preserved from error when she speaks definitively, the Supreme Pontiff is also preserved from error when he speaks with the voice of the whole Church (Pastor Æternus).

The college of bishops “in so far as it is composed of many members, is the expression of the variety and universality of the People of God; and of the unity of the flock of Christ, in so far as it is assembled under one head” (Lumen Gentium 22). It is necessary that everything in the Church to be done with the consent of the Roman Pontiff and the bishops, since they possess the authority of Christ. As St. Ignatius of Antioch said, “See that you all follow the bishop, even as Jesus Christ does the Father, and the presbytery as you would the apostles; and reverence the deacons, as being the institution of God. Let no man do anything connected with the Church without the bishop. Let that be deemed a proper Eucharist, which is either by the bishop, or by one to whom he has entrusted it. Wherever the bishop shall appear, there let the multitude also be; even as, wherever Jesus Christ is, there is the Catholic Church. It is not lawful without the bishop either to baptize or to celebrate a love-feast; but whatsoever he shall approve of, that is also pleasing to God, so that everything that is done may be secure and valid” (Letter to the Smyrnaeans 8).