The Church's Hierarchy
From the Catechism of the Catholic Church, Simplified
Diversity of Ministries (873-874)
A diversity of ministries exists which serves the Church's mission. To some (the apostles and their successors), Christ entrusted the office of teaching, sanctifying, and governing. The laity have their own roles. From both hierarchy and laity come Christian faithful who are consecrated to God and serve the Church through the profession of the evangelical councils (Canon 207). Christ established a variety of offices for the good of all. Those who hold offices invested with sacred powers must dedicate themselves to the salvation of all.
Receiving a Mandate - Holy Orders (875)
Faith comes from hearing. No one can "hear without a preacher" and no preacher can give himself a mandate. Only from Christ can ministers receive the mission and sacred power to "act in the person of Christ." This ministry is called "a sacrament" and is conferred by a special sacrament (Holy Orders).
A Service (876)
Besides having a sacramental nature, Church ministry must also have the character of service. Just as Christ took "the form of a slave" (Phil 2:7), so the minister must be a "slave of Christ."
A College of Service (877)
Church ministry has a collegial character. Jesus chose the twelve apostles and sent them out together to serve the faithful and to witness to the communion of the Trinity. Therefore, every bishop has his ministry only within the episcopal college in union with the Pope, and every priest serves in the presbyterate only in union with the diocesan bishop.
A Personal Quality (878-879)
Church ministry also has a personal character, because each person is to be a personal witness with a personal responsibility. Each person acts in Christ's name, e.g. "I absolve you."
Sacramental ministry is both collegial (exercised in communion) and personal (in Christ's name). Bishops are bonded within the college and within their head, the Pope. The bishop must care for his diocese and have solicitude for the whole Church.
The Apostolic College (880-881)
Christ constituted the twelve apostles as a college, a permanent assembly with Peter as the head. Therefore, Peter's successor (the bishop of Rome) and the apostles' successors (the other bishops) are united to one another in the episcopal college (Second Vatican Council).
Christ bestowed the power to bind and to loose upon Peter himself (Mt 16:19) and then upon all the apostles, including Peter (Mt 18:18). This pastoral office of Peter and of the other apostles belongs to the Church's very foundation and continues with the bishops under the primacy of the Pope.
Foundation of Unity (882)
The Pope, the bishop of Rome, is Peter's successor and the visible foundation of unity (for the bishops and for all the faithful). As pastor of the entire Church, the Pope has full, supreme, and universal power over the whole Church, which he can always exercise in an unhindered way (Second Vatican Council).
The College of Bishops (883-885)
Although the college of bishops has "supreme and full authority" over the Church, this authority cannot be exercised without the agreement of the Roman Pontiff.
The college of bishops exercises this power in a solemn manner in an ecumenical council (Canon 337). However, an ecumenical council must be confirmed or at least recognized as such by Peter's successor.
The college of bishops (comprised of many members) expresses the variety and the unity of the People of God assembled.
Unity in the Diocese and the Province (886-887)
The individual bishops are the visible foundation of unity in their dioceses. Each bishop must also have concern for the whole Church.
Neighboring dioceses form provinces or larger groupings (called patriarchates or regions). These bishops can meet in synods and provincial councils. Also, national conferences contribute to the concrete realization of the collegiate spirit.