"You are Peter, and upon this rock I will build my church"
Just as in the Gospel, the Lord so disposing, St. Peter and the other apostles constitute one apostolic college, so in a similar way the Roman Pontiff, the successor of Peter, and the bishops, the successors of the apostles, are joined together. Indeed, the very ancient practice whereby bishops duly established in all parts of the world were in communion with one another and with the Bishop of Rome in a bond of unity, charity and peace, and also the councils assembled together, in which more profound issues were settled in common, the opinion of the many having been prudently considered, both of these factors are already an indication of the collegiate character and aspect of the Episcopal order; and the ecumenical councils held in the course of centuries are also manifest proof of that same character. And it is intimated also in the practice, introduced in ancient times, of summoning several bishops to take part in the elevation of the newly elected to the ministry of the high priesthood. Hence, one is constituted a member of the Episcopal body in virtue of sacramental consecration and hierarchical communion with the head and members of the body.
But the college or body of bishops has no authority unless it is understood together with the Roman Pontiff, the successor of Peter as its head. The pope's power of primacy over all, both pastors and faithful, remains whole and intact. In virtue of his office, that is as Vicar of Christ and pastor of the whole Church, the Roman Pontiff has full, supreme and universal power over the Church. And he is always free to exercise this power. The order of bishops, which succeeds to the college of apostles and gives this apostolic body continued existence, is also the subject of supreme and full power over the universal Church, provided we understand this body together with its head the Roman Pontiff and never without this head. This power can be exercised only with the consent of the Roman Pontiff. For our Lord placed Simon alone as the rock and the bearer of the keys of the Church, and made him shepherd of the whole flock;(Jn 21,15f.) it is evident, however, that the power of binding and loosing, which was given to Peter,(Mt 16,19) was granted also to the college of apostles, joined with their head.( Mt 18,18; 28,16-20) This college, insofar as it is composed of many, expresses the variety and universality of the People of God, but insofar as it is assembled under one head, it expresses the unity of the flock of Christ.
~Pope Pius XI