THE UNITY OF THE CHURCH. — The Church is one, that is, undivided in itself and distinct from every other society. Therefore unity is an essential property of the Church and one of its distinguishing marks. The unity of the Church can be considered from within, that is, as it appears to the consciousness of itself (a rather dogmatic point of view); and from without, as it is manifested to those outside it (a rather apologetic point of view).
I. UNITY AS AN ESSENTIAL PROPERTY
1. Notion of the Unity of the Church
The unity of the Church is determined by its nature as a supernatural society founded by the Son of God. Just as the human race forms a unity of all the descendants of the first Adam and of “the mother of all the living” (Gen. 3:20), Eve, so the Church, as a society or community of the reborn, forms a unity of all the descendants of the second Adam, Christ, children of the second Eve, Mary, who is both the representative and the type of the Church (John 19:25-27; Apoc. 12). The Church is therefore one in Christ, as also in its priesthood and sacrifice, which is that of Christ. It is one in its Sacraments, especially in Baptism, by which man is incorporated into the unity of the Church and separated from the rest of humanity. It is one also in the Sacrament of Order, by which there is a unity with the past, the apostolic succession, and which is the indispensable condition for the Sacrament of Sacraments, the Eucharist, which unites with Christ and with all who are in Christ; hence the Eucharist is pre-eminently the Sacrament of unity.The Church is one in its entire ontological reality; it is also one in its truth, in its magisterium, and in its faith. Moreover, the Church is one in its organic hierarchical government. The unity of the magisterium and of the government is essentially concentrated in the one visible head of the Church, the Roman Pontiff, Vicar of the one invisible Head, Christ, and the sole successor of Peter, to whom the principle of apostolic succession goes back. The characteristic unity of the Catholic hierarchy, of bishops and priests, and of Catholic laity, consists in union with the successor of St. Peter.
Other related notions fall within the scope of unity. The unity of the Church is its unity insofar as it excludes any other similar unity. Then the unity of the Church can be considered in the succession of time, inasmuch as today’s Church is identical with that of yesterday and tomorrow (v. APOSTOLICITY OF THE CHURCH); it can be considered in the grouping of many classes into a whole, in its geographical extension among the different peoples and nations (v. CATHOLICITY OF THE CHURCH); and it can be considered in its spiritual depth, that is, as union with God through the grace of Christ (v. HOLINESS OF THE CHURCH). In short, the unity of the Church as such concerns all the bonds by which it is joined as a body to its Head, Jesus Christ; a truth recalled by St. Paul in Col. 2:19, exhorting one to “hold fast to the Head, from whom the whole body, nourished and knit together through its joints and ligaments, grows with a growth that is from God.” The proximate efficient cause of the unity of the Church is the will of Christ, who intended to found one Church; the ultimate cause is the benevolent will of the triune God, Father, Son, and Holy Spirit, source and ultimate foundation, in His one divine essence and in His free will, of every organic unity that exists; the final cause is indicated by St. Paul when he states that all things will be subjected to the Son, as the Son will be subjected to the Father, “that God may be all in all” (1 Cor. 15:28).
2. The Sources of Revelation on the Unity of the Church
a) Holy Scripture. — In the Old Testament the Church is prefigured as one in the ark of Noah, the only one saved from the universal flood; in the one chosen people, saved from the original Egyptian bondage and led through the desert into the promised land; the Church is spoken of when Isaiah announces that “in the last days the mountain of the house of the Lord shall be established as the highest of the mountains” (Is. 2:2). In the Song of Songs the bride is spoken of as a figure of the Church: “One is my dove, my perfect one, she is the only one of her mother, the choice one of her that bore her” (Cant. 6:8). In the New Testament, Jesus speaks twice of the Church, and uses the definite article (Matt. 16:18 and 18:17). He expressly says that He intended to build “His Church” upon Peter the rock, thus a single Church, distinct from any other that might claim to be founded on the “Son of the living God” (Matt. 16:16). St. John reports Jesus’ discourse, in which He calls Himself “the good shepherd” and predicts that there “shall be one fold and one shepherd” (John 10:11, 14, 16), a fold that the risen Jesus entrusts, with all His “lambs” and all His “sheep,” to the care of Peter (John 21:15 ff.).St. Paul speaks of the Church in the singular, meaning the Church “one and universal,” or of the Churches in the plural, in the sense of particular or local Churches, which are part of the same Church (e.g., Rom. 16:16: “All the churches of Christ salute you”); therefore when he speaks in the singular, the Apostle indicates the Church as one: “Christ is the head of the Church” (Eph. 5:23), which is, according to the same Apostle, “the body” of Christ, “and He is the saviour of the body” (ibid., V. 23); he immediately adds: “Husbands, love your wives, as Christ loved the Church and gave Himself up for her...” (ibid., V. 25); “for no man ever hates his own flesh, but nourishes and cherishes it, as Christ does the Church, because we are members of His body, of His flesh and of His bones” (ibid., vv. 29-30). St. Paul speaks of the Church as “the bride of Christ”; with this he demonstrates its unity and uniqueness. The bride, being in herself a physical person, is joined to the bridegroom, another physical person, by bonds that are first of all moral; but, moreover, “the two shall become one flesh” (Matt. 19:5; Gen. 2:24; Eph. 5:31). The body, distinguished by the head, forms, together with it, a unity that is more than moral, that is, organic and physical. From the intertwining of these two images it follows that the unity of the Church is more than merely moral (cf. encycl. Mystici Corporis: AAS, 35 [1943], p. 222).
According to the same St. Paul, the conscious moral union of Christians must correspond to the ontological unity of the Church; hence he exhorts the Ephesians to be “eager to maintain the unity of the Spirit in the bond of peace. There is one body and one Spirit, just as you were called to the one hope that belongs to your call, one Lord, one faith, one baptism, one God and Father of all, who is above all and through all and in all” (Eph. 4:3-6; cf. 1:22-23). In the text cited some interpreters understand “Spirit” as referring to the Holy Spirit. The unity of the Church therefore comprises the body and the spirit of the faithful, consisting in faith and Baptism and, as is even more clearly evident from 1 Cor. 12:12-13, in the bond with the Holy Spirit, with Christ, and with God the Father: “For just as the body is one and has many members, and all the members of the body, though many, are one body, so it is with Christ. For by one Spirit we were all baptized into one body—Jews or Greeks, slaves or free—and all were made to drink of one Spirit.” And just as in Baptism, so in the Eucharist the unity of the Church is manifested: “Because there is one bread, we who are many are one body, for we all partake of the one bread” (1 Cor. 10:17).
b) Definitions and Documents of the Church. — As in the Apostles’ Creed, so in all the creeds the profession of faith is made “in the Church”—not “in the Churches,” “in one Church,” “in the one Church.” In the Constantinopolitan Creed: “in one, holy, catholic, and apostolic Church” (Denz.-U., 86). In the profession prescribed for the Waldensians (1208, under Innocent III): “We confess
a Church not of heretics, but the holy Roman, Catholic, and Apostolic Church (Denz-U, 423). Famous is the bull *Unam sanctam* of 1302 by Boniface VIII, in which the following passages are applied to the Church: Cant. 6:8, Ps. 21:21: *"Save me from the lion’s mouth; my darling from the horns of the wild oxen"* (Denz-U, 468), John 19:23: the *"seamless tunic"*; *"thus of the Church there is one and only one body, one head, not two heads like a monster, that is, Christ and the vicar of Christ Peter, and the successor of Peter."*
Three other documents must be recalled: the letter of the Holy Office on the so-called *C.* (unicity) of 1864 (Denz-U, 1686), Leo XIII’s encyclical *Satis cognitum* (q.v.) of 1896 on the *C.* of the Church, an invitation for all to return to unity (Denz-U, 1954 ff.), and Pius XII’s encyclical *Mystici Corporis Christi, quod est Ecclesia* of 1943 (AAS, 35 [1943], pp. 193 ff.).
---
c) Christian Antiquity. — Very clear is the testimony of Christian antiquity and the Holy Fathers regarding the *C.* of the Church. Already in the *Didache* one sees, in connection with the Eucharist, in the one bread, gathered from many grains, a symbol of the unification of men in the Church (9:4; 10:5). St. Ignatius not only insists on the *C.* of the particular Church, with its unity under a single bishop and his clergy in the Eucharistic bread (e.g., *Philad.* 4; *Eph.* 20:2), but also speaks of the *"one body of the Church"* of Christ in general (e.g., *Smirn.* 1:2). In the *Shepherd of Hermas*, *"the tower"* is the Church (*Vis.* 3:5,1; *Sim.* 9:17,4). For St. Irenaeus, the Church *"dwells in one house,"* has one soul and the same heart, *"proclaims the faith and hands it on,"* possessing *"one mouth"* (Adv. haer. I, 10,2). For Clement of Alexandria, just as there is one Father, one Word, one Holy Spirit, so *"she becomes one virgin mother: I love to call her the Church"* (Paedag. I, 6,42,1). And he holds that *"the true Church is one... the one which heresies strive to cut into many"* (Strom. VII, 17). According to Tertullian, all Churches descend from the first Church of the Apostles; they are *"first and apostolic"* if all together they prove their unity in peace and fraternity (De praescr. haer. 20,4).
The clearest testimony comes from St. Cyprian, both in his letters and in *De catholicae Ecclesiae unitate*. He writes: *"God is one, and Christ is one, and the Church is one, and one is the See founded on Peter by the voice of the Lord. One cannot establish or be born a new priesthood outside the one altar and the one priesthood. Whoever gathers elsewhere scatters"* (Ep. 43,5). Or again: *"The Church is one, which cannot be one (i.e., the same) inside and outside. If, therefore, it is with Novatian, it was not with Cornelius (the Pope)"* (Ep. 69,3). In *De cath. Eccl. unitate*, ch. 5: *"The episcopate is one, of which each bishop holds a share in solidarity. The Church is one...; the Church, illumined by the light of the Lord, extends its rays throughout the world: thus the light is one, diffused everywhere, and the unity of the body is not severed."* In the text, St. Cyprian cites Cant. 6:8 and Eph. 4:4 and compares the Church to a fruitful mother, the Church as the spouse of Christ, and sees it prefigured in the ark of Noah (ibid. 6; cf. however PRIMACY OF ST. PETER AND OF THE ROMAN PONTIFF).
Among the great Eastern Fathers and Doctors of the 4th and 5th centuries, numerous testimonies on the *C.* of faith and communion of the universal Church can be gathered. The Roman Primacy as a principle of *C.* is found more explicitly in practice (doctrinal and disciplinary appeals to the supreme authority) than in doctrine. On the *C.* of the Body of Christ, St. Athanasius, St. Basil, St. Cyril of Jerusalem (explaining the Symbol), St. Gregory Nazianzen, St. Epiphanius, and St. John Chrysostom—who especially emphasizes the unity of communion and charity—are very explicit; so too is St. Cyril of Alexandria. The Western Doctors of the same period also highlight the *C.* of the Body of Christ: St. Hilary, St. Ambrose, St. Jerome. One of the clearest on this point is St. Optatus of Milevis, who holds that Peter, head of all the Apostles, called therefore Cephas, was bishop of Rome *"in whose See the unity is preserved by all, in opposition to schisms"* (Contra Parmenianum Donatistam II, 2).
The richest doctrine, however, is that of St. Augustine, who illustrates the *C.* of the Church with various images drawn from Holy Scripture, and insists, in the struggle against the Donatists and Pelagians, on the doctrinal and disciplinary primacy of Rome as the center of unity; this doctrine was later clearly expressed by St. Leo the Great, who explained his succession by affirming that Peter was elected *"so that, although in the people of God there are many priests and many shepherds, all are properly ruled by Peter"* (Serm. IV, 2).
d) Theologians. — In the Middle Ages, the theology of the *C.* of the Church gradually developed. In St. Thomas, one finds the broad outlines of the doctrine on the *C.* of the Body of Christ (Sum. Theol. III, q. 8). Notable is James of Viterbo’s *De regimine christiano* (1301–1302) (q.v.), which devotes a special chapter (I, 3) to *C.*, seeing in the union of the multitude of the faithful rather an *"association"* than a *"unity."* The first complete exposition on a theological-canonical basis was written by John Torquemada (q.v.) in his *Summa de Ecclesia*, in which he vindicates *C.* against Western and Eastern schismatics.
In modern times, the great speculative theologians—Cajetan, de Lugo, Suárez (Disp. IX *de fide*)—expound the principles of the *C.* of the Church. Apologists, opposing the false notes advanced by Protestants, set forth the true notes, first among them *C.* as understood by Catholic doctrine. Suárez develops this argument polemically in his *Defensio fidei adversus Anglos*; so too do St. Robert Bellarmine and Cardinal du Perron (against King James of England’s theory that the Church, in its *C.*, was like a confederation of religious societies agreeing on a minimum of beliefs), and the Jansenist P. Nicole in his treatise *De l’unité de l’Église ou Réfutation du nouveau système de M. Jurieu* (Paris 1687). In more recent times, the notion of the *C.* of the Church has been re-examined especially under the influence of the revival of patristic studies. One must recall the famous book by J. A. Möhler (q.v.), *Die Einheit in der Kirche oder das Prinzip des Katholizismus, dargestellt im Geist der Kirchenväter der drei ersten Jahrhunderte* (1825), which, with great probability, inspired the modern ecclesiologist of the Russian dissenters A. S. Khomyakov in his brief treatise *The Church is One* (c. 1845). Before and after the Vatican Council, up to the present day, many treatises *De Ecclesia* have appeared that deal extensively with *C.* But the impetus for deeper investigations into the *C.* of the Church has come from the so-called *"ecumenical movement"* (q.v.) among Christians now divided into innumerable denominations.
---
II. *C.* AS A DISTINCTIVE NOTE. —
3. Disunion
To *C.* are opposed schism (q.v.; cf. 1 Cor 1:10 ff.), heresy (q.v.), and secularization, i.e., the gradual separation from the entire work of the Church.2. False concepts of *C.* — These have arisen over the centuries, either from the desire to justify one’s own schismatic or heretical position or from the attempt by Catholics to combat divisions or clarify the traditional concept of *C.* St. Cyprian, for example, clarified against the schism of Novatian many essential features of ecclesiastical *C.*, yet did not always express with sufficient clarity and precision that the unity of governance in the Church finds its full realization in the perpetuity of the Primacy of Peter. Thus, in modern times, Möhler, in explaining to Protestants the true *C.* of the Church, emphasized too exclusively the internal principle of *C.*, namely the Holy Spirit, which achieves mystical unity, neglecting the external and visible aspect; he thus arrived at a conception similar to that of St. Cyprian, which he later corrected and completed in his subsequent work, the *Symbolik* (1832).
Medieval conciliarism (v.), which placed the unity and authority of general councils above that of the Pope, owes much to the Western Schism (v.). A similar conciliarism is found among dissident Eastern scholars, who hold that individual autocephalous national Churches, independent of one another in governance, form a confederation of communities linked only by rather weak bonds of charity and, occasionally, by the exchange of ideas. This is a highly imperfect form of unity, which not infrequently becomes disunity and even schism (as, for instance, the present hierarchy of the patriarchal Church of Moscow is in a state of schism vis-à-vis the hierarchy of Metropolitan Anastasius, formerly resident in Karlovitsi in Yugoslavia and now in New York; the Church of Moscow is also openly at odds with the “Ecumenical Patriarch” of Constantinople).
The Easterners, therefore, have begun to conceive of the unity of the Church (u. d. C.)—especially since the time of the Slavophile Khomyakov (v.)—in a vague and Protestantizing sense as “sobornost’” (i.e., etymologically, “conciliarity,” though historically identical with “catholicity”), meaning “unity in freedom and love,” thereby relegating the visible unity of the Church to the background. This conception is already very close to the Protestant view, which sees the unity of the Church primarily in the invisible elements of the Body of Christ.
While dissident Easterners still exclude Catholics and Protestants from the unity of the true Church—i.e., their own—on the grounds that Catholics, according to Khomyakov, have exaggerated the principle of unity and Protestants that of freedom, ecumenism, on the other hand, is based on the so-called “branches” theory, according to which the Christian confessions are branches of the same tree. This theory was condemned by Pius IX in 1864, insofar as it teaches that the universal unity of the Church should result from the union of three Christian communities: the Roman Catholic, the Greek-Schismatic, and the Anglican. Vladimir Soloviev has sometimes expressed himself as if the universal unity of the Church were to result only from the future union of Catholics, dissident Byzantine-Slavs, and Protestants; hence his axiom, “ceterum censeo instaurandam esse Ecclesiae unitatem,” is true only in the sense that unity must be restored by the return of the separated to II.
3. **Apologetic value of unity.** – Unity is not only an essential property of the Church but, for all who are outside it, a sign of recognition and a path to finding the true and one Church. It is: a) the most comprehensive of the notes; the other three (or more) notes may be regarded as particular cases of unity (v. supra); b) true and full unity results only from the sum of all the bonds that essentially exist in the Church (cf. Col. 2:19), namely, the bonds of faith, sacrifice and the Sacraments, and of a single united governance.
**III. Realization of the unity of the Church.** – Besides the efforts and acts of union on the part of the Catholic Church—especially the Papacy, which the Russian Chaadaev (1794–1856) defined as “the visible sign of unity and, since separation has occurred, also of reunion”—there are also attempts at union on the part of the dissidents, with their successors down to present-day ecumenism. These latter are marked by genuine impulses but are essentially fruitless, inasmuch as they seek to achieve unity without its foundation—namely, the stone placed by Christ Himself as the basis of His Church.
No one can deny that there is more unity in the Catholic Church than in the dissident Eastern communities, and more in these than among the Protestants of the various denominations. Unable to deny the fact of the greatest unity in the Catholic Church, the dissidents sometimes try to invalidate its spontaneous and natural apologetic value by asserting that Catholic unity is rather the effect of external coercion than the fruit of inner conviction.
To bring the separated back to unity, a twofold kind of centripetal force is required: a) the objective forces instituted by Christ Himself, namely, inward grace and the visible rock of Peter; b) the subjective forces, namely, the freedom to cooperate and the exercise of unitive Christian virtues—especially humility and fraternal charity—on both sides. This must be done in opposition to the centrifugal forces of pride and particularism, granting to all in the common house of God the freedom—wherever the obligatory unity of dogma is not at stake—of rites, disciplines, and ancient venerable traditions. The “pre-eminent” unitive and centripetal force was taught by Jesus in the priestly prayer: “That they may all be one, as thou, Father, in me and I in thee, that they also may be one in us” (Jn. 17:21).
**