Apologeticae sive Theologiae Fundamentalis, Tomus II (Pars Altera): Demonstratio Catholica

The social communion of the Church consists in this, that all the faithful, through one and the same hierarchical government, are gathered together into one and the same organism, with every schism excluded. The following expressly require this unity of social communion:

1. Christ, because He instituted the Church as a society properly and strictly so called, and everywhere describes it by the metaphors of a kingdom, a city, a house, a sheepfold, a flock. All of which presuppose the social unity of the Church. To obtain this unity among His own and to strengthen it forever, Christ poured forth a prayer to the Father: "Holy Father, keep them [the apostles] in thy name, whom thou hast given me, that they may be one, as we also are … And not for them only do I pray, but for them also who through their word shall believe in me: that they all may be one, as thou, Father, in me, and I in thee, that they also may be one in us: that the world may believe that thou hast sent me. And the glory which thou hast given me, I have given to them: that they may be one, as we also are one: that they may be made perfect in one and the world may know that thou hast sent me and hast loved them, as thou hast also loved me."¹

2. Paul. For he describes the Church, as we already know, very often by the metaphor of the human body, signifying that it is one moral whole, just as the human body is one physical whole. "For as the body is one and has many members, and all the members of the body, whereas they are many, yet are one body: so also is Christ [the mystical = the Church]. For in one Spirit were we all baptized into one body … The members indeed are many, but one body. And the eye cannot say to the hand: I have no need of thy works: or again the head to the feet: You are not necessary to me … that there may be no schism in the body, but the members might be mutually solicitous one for another … But you are the body of Christ, and members of member.² Just as all the members of the body coalesce in an orderly and intimate manner into one body; just as the individual members have their own office and are helped and fostered by the other members; just as there is no schism in the body, but a mutual unity of communion and charity: so also is the mystical body of Christ, i. e. the Church.

3. Christian antiquity. The Fathers exceedingly abhorred schisms and forbade every communion of the faithful with schismatics, e. g. already s. Ignatius: "If anyone follows one who makes a schism, he shall not obtain the inheritance of the divine kingdom."³ The faithful who were about to travel abroad, that they might be admitted in foreign churches, were furnished with letters, as they called them, canonical communicatory or formatae.⁴ By similar letters given and received the bishops testified to union with other bishops and other churches;⁵ but above all they proved social communion with the universal Church by formatae sent to the Roman pontiff and received in turn from him.⁶

In truth, the unity of creedal confession and of the social communion of the whole Church is ultimately effected, preserved, and demonstrated solely by union with the supreme pontiff. The members of the human body constitute one body, inasmuch as through every joint of supply they cohere to the head;⁷ the faithful of the Church visibly constitute one mystical body of Christ, inasmuch as through the bishops they cohere to the supreme pontiff, the visible head of the Church.