Against Radical Traditionalism: "Satis Cognitum" (1896) - Pope Leo XIII

Full encyclical text here: https://www.vatican.va/content/leo-xiii/en/encyclicals/documents/hf_l-xiii_enc_29061896_satis-cognitum.html

[T]hose who arbitrarily conjure up and picture to themselves a hidden and invisible Church are in grievous and pernicious error: as also are those who regard the Church as a human institution which claims a certain obedience in discipline and external duties, but which is without the perennial communication of the gifts of divine grace, and without all that which testifies by constant and undoubted signs to the existence of that life which is drawn from God. It is assuredly as impossible that the Church of Jesus Christ can be the one or the other, as that man should be a body alone or a soul alone. The connection and union of both elements is as absolutely necessary to the true Church as the intimate union of the soul and body is to human nature.

Scattered and separated members cannot possibly cohere with the head so as to make one body. But St. Paul says: “All members of the body, whereas they are many, yet are one body, so also is Christ” (I Cor. xii., 12). Wherefore this mystical body, he declares, is “compacted and fitly jointed together. The head, Christ: from whom the whole body, being compacted and fitly jointed together, by what every joint supplieth according to the operation in the measure of every part” (Eph. iv., 15-16). And so dispersed members, separated one from the other, cannot be united with one and the same head. “There is one God, and one Christ; and His Church is one and the faith is one; and one the people, joined together in the solid unity of the body in the bond of concord. This unity cannot be broken, nor the one body divided by the separation of its constituent parts” (S. Cyprianus, De Cath. Eccl. Unitateccl. Unitate, n. 23).

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.

Maximus the Abbot teaches that obedience to the Roman Pontiff is the proof of the true faith and of legitimate communion. Therefore if a man does not want to be, or to be called, a heretic, let him not strive to please this or that man…but let him hasten before all things to be in communion with the Roman See. If he be in communion with it, he should be acknowledged by all and everywhere as faithful and orthodox. He speaks in vain who tries to persuade me of the orthodoxy of those who, like himself, refuse obedience to his Holiness the Pope of the most holy Church of Rome: that is to the Apostolic See.”

Above all things the need of union between the bishops and the successors of Peter is clear and undeniable. This bond once broken, Christians would be separated and scattered, and would in no wise form one body and one flock. "The safety of the Church depends on the dignity of the chief priest, to whom if an extraordinary and supreme power is not given, there are as many schisms to be expected in the Church as there are priests" (S. Hieronymus, Dialog, contra Luciferianos, n. 9).

From this it must be clearly understood that Bishops are deprived of the right and power of ruling, if they deliberately secede from Peter and his successors; because, by this secession, they are separated from the foundation on which the whole edifice must rest. They are therefore outside the edifice itself; and for this very reason they are separated from the fold, whose leader is the Chief Pastor; they are exiled from the Kingdom, the keys of which were given by Christ to Peter alone.

Hence the teaching of Cyprian, that heresy and schism arise and are begotten from the fact that due obedience is refused to the supreme authority. "Heresies and schisms have no other origin than that obedience is refused to the priest of God, and that men lose sight of the fact that there is one judge in the place of Christ in this world" (Epist. xii. ad Cornelium, n. 5). No one, therefore, unless in communion with Peter can share in his authority, since it is absurd to imagine that he who is outside can command in the Church. Wherefore Optatus of Milevis blamed the Donatists for this reason: "Against which ages (of hell) we read that Peter received the saving keys, that is to say, our prince, to whom it was said by Christ: `To thee will I give the keys of the Kingdom of Heaven, and the gates of Hell shall not conquer them.' Whence is it therefore that you strive to obtain for yourselves the keys of the Kingdom of Heaven-you who fight against the chair of Peter?" (Lib. ii., n. 4-5).

Nor does it beget any confusion in the administration that Christians are bound to obey a twofold authority. We are prohibited in the first place by Divine Wisdom from entertaining any such thought, since this form of government was constituted by the counsel of God Himself. In the second place we must note that the due order of things and their mutual relations are disturbed if there be a twofold magistracy of the same rank set over a people, neither of which is amenable to the other. [...] "It is not congruous that two superiors with equal authority should be placed over the same flock; but that two, one of whom is higher than the other, should be placed over the same people is not incongruous." (St. Thomas in iv Sent, dist. xvii., a. 4, ad q. 4, ad 3).

We lovingly address to all the words of St. Augustine: "Let us love the Lord our God; let us love His Church; the Lord as our Father, the Church as our Mother. Let no one say, I go indeed to idols, I consult fortune-tellers and soothsayers; but I leave not the Church of God: I am a Catholic. Clinging to thy Mother, thou offendest thy Father. Another, too, says: 'Far be it from me; I do not consult fortune - telling, I seek not soothsaying, I seek not profane divinations, I go not to the worship of devils, I serve not stones: but I am on the side of Donatus.' What doth it profit thee not to offend the Father, who avenges an offence against the Mother? What doth it profit to confess the Lord, to honour God, to preach Him, to acknowledge His Son, and to confess that He sits on the right hand of the Father, if you blaspheme His Church? . . . If you had a beneficent friend, whom you honoured daily - and even once calumniated his spouse, would you ever enter his house? Hold fast, therefore, O dearly beloved, hold fast altogether God as your Father, and the Church as your Mother" (Enarratio in Psal. lxxxviii., sermo ii., n. 14).