When Christ instituted the Twelve, “he constituted [them] in the form of a college or permanent assembly, at the head of which he placed Peter, chosen from among them.” Just as “by the Lord’s institution, St. Peter and the rest of the apostles constitute a single apostolic college, so in like fashion the Roman Pontiff, Peter’s successor, and the bishops, the successors of the apostles, are related with and united to one another.”
The Lord made Simon alone, whom he named Peter, the “rock” of his Church. He gave him the keys of his Church and instituted him shepherd of the whole flock. “The office of binding and loosing which was given to Peter was also assigned to the college of apostles united to its head.”This pastoral office of Peter and the other apostles belongs to the Church’s very foundation and is continued by the bishops under the primacy of the Pope.
The Pope, Bishop of Rome and Peter’s successor, “is the perpetual and visible source and foundation of the unity both of the bishops and of the whole company of the faithful.” “For the Roman Pontiff, by reason of his office as Vicar of Christ, and as pastor of the entire Church has full, supreme, and universal power over the whole Church, a power which he can always exercise unhindered.”
“The college or body of bishops has no authority unless united with the Roman Pontiff, Peter’s successor, as its head.” As such, this college has “supreme and full authority over the universal Church; but this power cannot be exercised without the agreement of the Roman Pontiff.”
“The college of bishops exercises power over the universal Church in a solemn manner in an ecumenical council.” But “there never is an ecumenical council which is not confirmed or at least recognized as such by Peter’s successor.”
“This college, 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.”
“The individual bishops are the visible source and foundation of unity in their own particular Churches.” As such, they “exercise their pastoral office over the portion of the People of God assigned to them,” assisted by priests and deacons. But, as a member of the episcopal college, each bishop shares in the concern for all the Churches. The bishops exercise this care first “by ruling well their own Churches as portions of the universal Church,” and so contributing “to the welfare of the whole Mystical Body, which, from another point of view, is a corporate body of Churches.” They extend it especially to the poor, to those persecuted for the faith, as well as to missionaries who are working throughout the world.
Neighboring particular Churches who share the same culture form ecclesiastical provinces or larger groupings called patriarchates or regions. The bishops of these groupings can meet in synods or provincial councils. “In a like fashion, the episcopal conferences at the present time are in a position to contribute in many and fruitful ways to the concrete realization of the collegiate spirit.”
From the Catechism of the Catholic Church 880-887