10 But as this heavenly doctrine was never left to the arbitrary judgment of private individuals, but, in the beginning delivered by Jesus Christ, was afterwards committed by Him exclusively to the Magisterium already named, so the power of performing and administering the divine mysteries, together with the authority of ruling and governing, was not bestowed by God on all Christians indiscriminately, but on certain chosen persons. For to the Apostles and their legitimate successors alone these words have reference: "Going into the whole world preach the Gospel." "Baptizing them." "Do this in commemoration of Me." "Whose sins you shall forgive they are forgiven them." And in like manner He ordered the Apostles only and those who should lawfully succeed them to feed - that is to govern with authority - all Christian souls. Whence it also follows that it is necessarily the duty of Christians to be subject and to obey. And these duties of the Apostolic office are, in general, all included in the words of St. Paul: "Let a man so account of us as of the ministers of Christ, and the dispensers of the mysteries of God" (I Cor . iv., I). Wherefore Jesus Christ bade all men, present and future, follow Him as their leader and Saviour; and this, not merely as individuals, but as forming a society, organized and united in mind. In this way a duly constituted society should exist, formed out of the divided multitude of peoples, one in faith, one in end, one in the participation of the means adapted to the attainment of the end, and one as subject to one and the same authority. To this end He established in the Church all principles which necessarily tend to make organized human societies, and through which they attain the perfection proper to each. That is, in it (the Church), all who wished to be the sons of God by adoption might attain to the perfection demanded by their high calling, and might obtain salvation. The Church, therefore, as we have said, is man's guide to whatever pertains to Heaven. This is the office appointed unto it by God: that it may watch over and may order all that concerns religion, and may, without let or hindrance, exercise, according to its judgment, its charge over Christianity. Wherefore they who pretend that the Church has any wish to interfere in Civil matters, or to infringe upon the rights of the State, know it not, or wickedly calumniate it. God indeed even made the Church a society far more perfect than any other. For the end for which the Church exists is as much higher than the end of other societies as divine grace is above nature, as immortal blessings are above the transitory things on the earth. Therefore the Church is a society divine in its origin, supernatural in its end and in means proximately adapted to the attainment of that end; but it is a human community inasmuch as it is composed of men. For this reason we find it called in Holy Writ by names indicating a perfect society. It is spoken of as the House of God, the city placed upon the mountain to which all nations must come. But it is also the fold presided over by one Shepherd, and into which all Christ's sheep must betake themselves. Yea, it is called the kingdom which God has raised up and which will stand for ever . Finally it is the body of Christ - that is, of course, His mystical body, but a body living and duly organized and composed of many members; members indeed which have not all the same functions, but which, united one to the other, are kept bound together by the guidance and authority of the head. Indeed no true and perfect human society can be conceived which is not governed by some supreme authority. Christ therefore must have given to His Church a supreme authority to which all Christians must render obedience. For this reason, as the unity of the faith is of necessity required for the unity of the church, inasmuch as it is the body of the faithful , so also for this same unity, inasmuch as the Church is a divinely constituted society, unity of government, which effects and involves unity of communion , is necessary jure divino . "The unity of the Church is manifested in the mutual connection or communication of its members, and likewise in the relation of all the members of the Church to one head" ( St. Thomas , 2a 2ae, 9, xxxix., a. I). From this it is easy to see that men can fall away from the unity of the Church by schism, as well as by heresy. "We think that this difference exists between heresy and schism" (writes St. Jerome): "heresy has no perfect dogmatic teaching, whereas schism, through some Episcopal dissent, also separates from the Church" (S. Hieronymus, Comment. in Epist. ad Titum , cap. iii., v. 10-11). In which judgment St. John Chrysostom concurs: "I say and protest (he writes) that it is as wrong to divide the Church as to fall into heresy" (Hom. xi., in Epist. ad Ephes ., n. 5). Wherefore as no heresy can ever be justifiable, so in like manner there can be no justification for schism. "There is nothing more grievous than the sacrilege of schism....there can be no just necessity for destroying the unity of the Church" (S. Augustinus, Contra Epistolam Parmeniani , lib. ii., cap. ii., n. 25).
Source: Satis Cognitum (Vatican.va)