So far we have concerned ourselves with the organization of the Catholic Church--its membership, its officers, the clergy, secular and regular, all culminating in the pope, the bishop of Rome. But why did this great institution exist? Why was it loved, venerated, and well served? The purpose of the Church, according to its own teaching, was to follow the instructions of its Divine Master, Jesus Christ, in saving souls. Only the Church might interpret those instructions; the Church alone might apply the means of salvation; outside the Church no one could be saved. [Footnote: Catholic theologians have recognized, however, the possibility of salvation of persons outside the visible Church. Thus, the catechism of Pope Pius X says: "Whoever, without any fault of his own, and in good faith, being outside the Church, happens to have been baptized or to have at least an implicit desire for baptism, and, furthermore, has been sincere in seeking to find the truth, and has done his best to do the will of God, such an one, although separated from the body of the Church, would still belong to her soul, and therefore be in the way of salvation."] The salvation of souls for eternity was thus the supreme business of the Church. [Sidenote: Theology] This salvation of souls involved a theology and a sacramental system, which we shall proceed to explain. Theology was the study of God. It sought to explain how and why man was created, what were his actual and desirable relations with God, what would be the fate of man in a future life. The most famous theologians of the Catholic Church, for example, St. Thomas Aquinas (d. 1274), studied carefully the teachings of Christ, the Bible, the early Christian writings, and the decrees of popes and councils, and drew therefrom elaborate explanations of Christian theology--the dogmas and faith of the Catholic Church. [Sidenote: The Sacramental System]