4 This same high idea is clearly brought out by the works of the Fathers, the laws of the Roman Pontiffs, and the Bishops, by the decrees of the Councils, and by the unanimous teaching of the Doctors and of the Catholic schools. Above all, the tradition of the Church with one voice proclaims that the priest is another Christ, and that the priesthood though exercised on earth merits to be numbered among the orders of heaven(4); because it is given to them to administer things that are wholly celestial and upon them is conferred a power that God has not trusted even to the angels(5); a power and ministry which regard the government of souls, and which is the art of arts.(6) Therefore, education, studies, customs, and whatever comprises the sacerdotal discipline have always been considered by the Church as belonging entirely to herself, not merely distinct, but altogether separate from the ordinary rules of secular life. This distinction and separation must, therefore, remain unaltered, even in our own times, and any tendency to accommodate or confound the ecclesiastical life and education with the secular life and education must be considered as reproved, not only by the traditions of Christian ages, but by the apostolic doctrine itself and the ordinances of Jesus Christ.
Source: Fin dal Principio (Vatican.va)