Successor to the Apostles:
Each bishop in the Catholic Church is a successor to the Apostles. Ordained by fellow bishops, who were themselves ordained by fellow bishops, each bishop can trace a direct, unbroken line of ordination back to the Apostles, a condition known as "apostolic succession." As with the original Apostles, the office of the bishop, the episcopate, is reserved to baptized males. While some of the Apostles (notably Saint Peter) were married, from an early point in the Church's history, the episcopacy was reserved to unmarried men. In the Eastern Church (Catholic and Orthodox), bishops are drawn from the ranks of monks.
Visible Source and Foundation of Unity of the Local Church:
Just as each of the Apostles went forth from Jerusalem to spread the Word of God by founding local churches, of which they became the head, so, too, the bishop today is the visible source of unity in his diocese, his local church. He is responsible for the spiritual and, to a certain extent, even the physical care of those in his diocese—first the Christians, but also anyone residing therein. He rules his diocese as a portion of the universal Church.
Herald of the Faith:
The first duty of the bishop is the spiritual welfare of those who reside in his diocese. That includes preaching the Gospel not only to the converted but, even more importantly, to the unconverted. In the day-to-day matters of life, the bishop guides his flock, to help them better understand the Christian faith and concretely translate it into action. He ordains priests and deacons to assist him in preaching the Gospel and celebrating the sacraments.
Steward of Grace:
"The Eucharist," the Catechism of the Catholic Church reminds us, "is the center of the life of the particular Church" or diocese. The bishop, as the supreme priest in his diocese, upon whose authority all other priests of the diocese must depend, holds the primary responsibility for ensuring that the sacraments are offered to the people. In the cases of the Sacrament of Confirmation, its celebration (in the Western Church) is normally reserved to the bishop, to emphasize his role as the steward of grace for his diocese.
Shepherd of Souls:
The bishop does not lead simply by example and by safeguarding the grace of the sacraments, however. He is also called to exercise the authority of the Apostles, which mean governing his local church and correcting those who are in error. When he acts in communion with the whole Church (in other words, when he does not teach something contrary to the Christian faith), he has the power to bind the consciences of the faithful in his diocese. Moreover, when all of the bishops act together, and their action is confirmed by the pope, their teaching on faith and morals is infallible, or free from error.