Unity in the Early Church
The concept of unity is foundational to the identity and mission of the Church as revealed in both the Old and New Testaments. The early Christian Church saw itself as the continuation and fulfillment of Israel’s covenant community, called to embody the oneness of God through communal and doctrinal unity. This unity was not merely ideal or symbolic but was understood as visible, sacramental, and institutional. From Christ’s high priestly prayer to the letters of the Apostles and the writings of the early Church Fathers, unity was viewed as a divine imperative rooted in the Eucharist and maintained through apostolic succession and ecclesial authority.
The Old Testament and the Unity of Israel
In the Old Testament, the people of Israel were called to unity under one God, one Law, one covenant, and one place of worship. The Shema (Deut. 6:4), “Hear, O Israel: The Lord our God, the Lord is one,” not only affirmed monotheism but also implied that God’s people must reflect this oneness in covenantal fidelity. Though the kingdom would eventually divide (1 Kgs 12), the ideal of a united Israel remained central to prophetic hope and messianic expectation (cf. Ezek. 37:15–28). Israel’s unity was both political and cultic, revolving around the Ark, the Temple, and the high priesthood—all symbols prefiguring the Church’s own visible unity in worship, doctrine, and leadership.
Christ’s Vision for Unity
In the New Testament, Christ’s vision of the Church as one is most poignantly captured in His high priestly prayer:
“That they may all be one; even as you, Father, are in me and I in you, that they also may be in us, so that the world may believe that you have sent me” (John 17:21).
This unity is not merely organizational but deeply theological—it mirrors the unity of the Trinity. Christ entrusted the Apostles with preserving this unity (Matt. 16:18–19; 18:17–18), promising to be with them as they exercised teaching and binding authority. The Eucharist became the central act of unity, fulfilling the Old Testament Passover and forming one body of believers (1 Cor. 10:16–17).
Pauline and Petrine Teachings on Unity
St. Paul passionately advocated for Church unity, warning against schisms and factions. In his first letter to the Corinthians, he writes:
“I appeal to you… that all of you agree, and that there be no divisions among you, but that you be united in the same mind and the same judgment” (1 Cor. 1:10).
Paul emphasized unity through “one body and one Spirit… one Lord, one faith, one baptism” (Eph. 4:4–5), identifying this unity as a gift of the Spirit to be maintained through humility, love, and apostolic teaching.
St. Peter, the leader of the Apostles, also exhorted Christians to “have unity of spirit, sympathy, love for one another” (1 Pet. 3:8). He played a central unifying role at the Council of Jerusalem (Acts 15), where apostolic authority settled doctrinal disputes. Peter’s leadership was not autocratic but pastoral, anchoring unity through communion in truth and charity.
The Apostolic Fathers: Unity and the Eucharist
The Apostolic Fathers saw unity as inseparable from the Eucharist and the episcopate. St. Ignatius of Antioch (d. c. 107), on his way to martyrdom, repeatedly emphasized unity under the bishop and warned against schismatics:
“Take heed, then, to have but one Eucharist. For there is one flesh of our Lord Jesus Christ, and one cup unto unity of His blood… There is one altar, even as there is one bishop, with his presbytery and the deacons” – Letter to the Philadelphians 4.1[^1].
In Letter to the Smyrnaeans 8.1–2, Ignatius writes:
“Wherever the bishop appears, there let the people be; just as wherever Jesus Christ is, there is the Catholic Church… It is not lawful apart from the bishop either to baptize or to hold a love-feast [Eucharist].”[^2]
Here, unity is not an abstract spiritual reality but is sacramentally and ecclesially expressed. The Eucharist unites the faithful in one body, but it must be celebrated under legitimate apostolic authority. Without this, any so-called unity is merely “in name only.”
The Pre-Nicene Fathers: Unity and the Bishop of Rome
As the Church expanded, disputes over doctrine and practice arose, yet unity was continually preserved through a visible communion centered on apostolic succession and, increasingly, the bishop of Rome. Pope Clement I (c. 96) wrote to the Corinthians to restore order in their community, urging obedience to legitimate presbyters:
“Our apostles knew through our Lord Jesus Christ that there would be strife for the office of the episcopate. For this reason… they appointed the aforesaid persons, and afterwards added instructions that when these should fall asleep, other approved men should succeed them” – 1 Clement 44:1–3[^3].
Clement’s intervention reveals a recognized Roman primacy, where the bishop of Rome could exercise corrective authority beyond his local church to preserve unity.
St. Irenaeus of Lyons (c. 180), writing against the Gnostics, declared:
“It is a matter of necessity that every Church should agree with this Church [Rome], on account of its preeminent authority” – Against Heresies 3.3.2[^4].
Irenaeus understood this agreement not as domination but as the safeguard of catholic unity, rooted in the succession from Peter and Paul.
Unity through Councils and Communication
The early Church preserved unity across a growing and diverse empire through synods, councils, epistles, and constant communication among bishops. The Council of Jerusalem (Acts 15) set the precedent, and regional synods followed, such as the Synod of Rome (c. 190) under Pope Victor I, addressing the date of Easter.
Dionysius of Corinth (c. 170) praised Pope Soter’s letter to the Corinthian Church and said:
“We received your letter… which we read aloud before the whole assembly, as we do with the letter of Clement” – cited in Eusebius, Church History 4.23.11[^5].
This illustrates how epistolary communication among churches, particularly from Rome, functioned as a stabilizing and unifying force.
Conclusion
The early Church viewed unity as essential to its identity and mission. Rooted in Old Testament covenantal oneness, fulfilled in Christ’s prayer and sacrifice, and actualized in the Eucharist and apostolic succession, this unity was both spiritual and institutional. The Church Fathers understood that without visible unity grounded in apostolic authority, the Church risked dissolving into fragmentation. Therefore, they emphasized unity under the bishop, especially the bishop of Rome, as well as through conciliar dialogue and fraternal correspondence. For the early Christians, to be in Christ was to be in communion—with the Eucharist, with the bishop, and with the universal Church.
Footnotes
[^1]: Ignatius of Antioch, Letter to the Philadelphians 4.1, in The Apostolic Fathers, trans. Bart D. Ehrman, Loeb Classical Library (Cambridge, MA: Harvard University Press, 2003).
[^2]: Ignatius of Antioch, Letter to the Smyrnaeans 8.1–2, ibid.
[^3]: Clement of Rome, 1 Clement 44:1–3, in The Apostolic Fathers, trans. Michael W. Holmes, 3rd ed. (Grand Rapids: Baker Academic, 2007).
[^4]: Irenaeus, Against Heresies 3.3.2, in The Ante-Nicene Fathers, vol. 1, ed. Alexander Roberts and James Donaldson (Peabody: Hendrickson, 1994).
[^5]: Eusebius, Church History 4.23.11, in Nicene and Post-Nicene Fathers, Second Series, Vol. 1, ed. Philip Schaff and Henry Wace (Peabody: Hendrickson, 1994).
Bible Verses:
John 17:20-21
“I ask not only on behalf of these, but also on behalf of those who will believe in me through their word, that they may all be one. As you, Father, are in me and I am in you, may they also be in us, so that the world may believe that you have sent me.”
1 Corinthians 1:10
“Now I appeal to you, brothers and sisters, by the name of our Lord Jesus Christ, that all of you be in agreement and that there be no divisions among you, but that you be united in the same mind and the same purpose.”
Ephesians 4:4-6
“There is one body and one Spirit, just as you were called to the one hope of your calling; one Lord, one faith, one baptism; one God and Father of all, who is above all and through all and in all.”
Romans 12:4-5
“For as in one body we have many members, and not all the members have the same function, so we, who are many, are one body in Christ, and individually we are members one of another.”
Colossians 3:14
“Above all, clothe yourselves with love, which binds everything together in perfect harmony.”
Philippians 2:1-2
“If then there is any encouragement in Christ, any consolation from love, any sharing in the Spirit, any compassion and sympathy, make my joy complete: be of the same mind, having the same love, being in full accord and of one mind.”
1 Peter 3:8
“Finally, all of you, have unity of spirit, sympathy, love for one another, a tender heart, and a humble mind.”
Acts 4:32
“Now the whole group of those who believed were of one heart and soul, and no one claimed private ownership of any possessions, but everything they owned was held in common.”
Church Father Quotes:
The Didache (Written ca. 50-70 A.D.)
“Thou shalt not desire a schism, but shalt reconcile those that strive. Thou shalt give righteous judgement; thou shalt favor no mans person in reproving transgression.” – Didache Chapter 4:3
“Thou shalt not be of two minds whether it shall be or not.” –Didache Chapter 4:4
Clement I of Rome (Martyred 96 A.D.)
“Love unites us to God.. Love makes no schism; love does not quarrel; love does everything in unity.” – The First Letter of Clement to the Corinthians
Ignatius of Antioch (35-107 A.D.)
“Wherever the bishop appears, there let the people be; just as wherever Jesus Christ is, there is the Catholic Church.” –Letter to the Smyrnaeans, 8:2
“Do nothing without the bishop, always keep your body as the temple of God, love unity, flee from divisions, be imitators of Jesus Christ, as he was imitator of the Father.”– Letter to the Philadelphians 7:1-2 (Written in 107 A.D.)
“For where there is division and wrath, God does not dwell. To all them that repent, the Lord grants forgiveness, if they tum in penitence to the unity of God, and to communion with the bishop.” –Letter to the Philadelphians 8:1 (Written 107 A.D.)
“Those indeed who belong to God and to Jesus Christ, they are with the Bishop. And those who repent and come to the unity of the Church, they too shall be of God and be living according to Jesus Christ. Be not deceived, my brethren: If anyone follows a schismatic, he will not inherit the kingdom of God; if anyone walks in strange doctrine (heresy), he has no part in the passion of Christ.” –Letter of Ignatius to the Philadelphians 3:2-3
(Written in 107 A.D.)
Irenaeus of Lyons (130-202 A.D.)
“The Church, though dispersed throughout the whole world, even to the ends of the earth, has received from the apostles and their disciples this faith.” –Against Heresies, Book I, Chapter 10
“A Christian shall also judge those who give rise to schisms.. . who look to their own advantage rather than the unity of the Church… For they can bring about no reformation of enough importance to compensate for the evil arising from their schism.” –Against Heresies 4:33:7-8 (Written in 189 A.D.)
Clement of Alexandria (150-215 A.D.)
“The whole Church is one, and this unity is the foundation of faith.” –Stromata, Book I, Chapter 21
“From what has been said, then, it seems clear to me that the true Church, that which is really ancient, is one; and in it are enrolled those who, in accord with a design (24), are just. . .. [S] We say, therefore, that in substance, in concept, in origin and in eminence, the ancient and Catholic Church is alone, gathering as it does into the unity of the one faith which results from the familiar covenants, – or rather, from the one covenant in different times, by the will of the one God and through the one Lord, – those already chosen, those predestined by God who knew before the foundation of the world that they would be just.” –Stromata 7:17:107:3
Tertullian of Carthage (155-240 A.D.)
“The Church is a unity, and cannot be broken; its members are bound to one another.” –On Prescription Against Heretics, 20
“[The apostles] founded churches in every city, from which all the other churches, one after another, derived the tradition of the faith, and the seeds of doctrine, and are every day deriving them, that they may become churches. Indeed, it is on this account only that they will be able to deem themselves apostolic, as being the offspring of apostolic churches. Every sort of thing must necessarily revert to its original for its classification. Therefore the churches, although they are so many and so great, comprise but the one primitive Church, [founded] by the apostles, from which they all [spring]. In this way, all are primitive, and all are apostolic, while they are all proved to be one in unity.” –Demurrer Against the Heretics 20 [A.D. 200]).
Cyprian of Carthage (200-258 A.D.)
“He can no longer have God for his Father, who has not the Church for his mother.”
-On the Unity of the Church, 6
“On Peter, he builds the Church (Matt, 16:18-19), and to him he gives the command to feed the sheep (John 21:17), and although he assigns a like power to all the apostles, yet he founded a single chair (cathedra), and he established by his own authority a source and an intrinsic reason for that unity. . . a primacy is given to Peter, whereby it is made clear that there is but one Church and one chair. If someone does not hold fast to this unity of Peter, can he imagine that he still holds the faith? If he deserts the chair of Peter upon whom the Church was built, can he still be confident that he is in the Church?” –The Unity of the Catholic Church 4 (Written 251 A.D.)
“There is one God and one Christ, and one Church, and one chair founded on Peter by the word of the Lord. It is not possible to set up another altar or for there to be another priesthood besides that one altar and that one priesthood. Whoever has gathered elsewhere is scattering.” –Letters 43 [40] :5 (Written 253 A.D.)
“There speaks Peter, upon whom the Church would be built. . . You ought to know, then that the Bishop is in the Church and the Church is in the Bishop; and if anyone is not with the Bishop, then he is not in the Church. . . For the Church is One and Catholic, is not split or divided, but is indeed united and joined by the cement of priests who adhere to one another.” –Letter to Florentius Pupianus 66 (69) :8 (Written 254 A.D.)
“The Church is one, and since she is one, she cannot be both within and without. For if she is with Novatian, then she is not with Pope Cornelius. If she is with Cornelius, who succeeded the bishop Fabian by lawful ordination. . . then Novatian is not in the Church; nor can he be reckoned as a bishop. since he -succeeding no one and despising the apostolic tradition- sprang only from himself. For he who has not been ordained in the Church can neither have nor hold to the Church in any way.” –Letters 75:3 (Written in 253 A.D.)
Athanasius of Alexandria (295-373 A.D.)
“The Church is the place where the unity of faith is maintained.” –On the Incarnation, 4
Cyril of Jerusalem (313-386 A.D.)
“Let us hold fast to the tradition of the Church, which preserves unity and truth.” –Catechetical Lectures, Lecture 18
Basil the Great (330-379 A.D.)
“Unity in essentials is the mark of the Church.” –On the Holy Spirit, 1:7
John Chrysostom (347-407 A.D.)
“For where there is the Church, there is the Spirit of God; and where the Spirit of God is, there is the Church.” –Homilies on the Acts of the Apostles, 2
Ambrose of Milan (340-397 A.D.)
“There is one Church, which is the body of Christ.” –On the Sacraments, Book V, Chapter 4
Rufinus of Aquileia (344-411 A.D.)
“This is that holy Church which is without spot or wrinkle. For many others have gathered together Churches, as Marcion, and Valentinus, and Ebion, and Manichæus, and Arius, and all the other heretics. . . But of this Church which keeps the faith of Christ entire, hear what the Holy Spirit says in the Canticles, ‘My dove is one; the perfect one of her mother is one.’” -Commentary on the Apostles’ Creed 39 (Written ca 407-409).
Augustine of Hippo (354-430 A.D.)
“This Church is holy, the one Church, the true Church, the Catholic Church, fighting as she does against all heresies. She can fight, but she cannot be beaten. All heresies are expelled from her, like the useless loppings pruned from a vine. She remains fixed in her root, in her vine, in her love. The gates of hell shall not conquer her.” –Sermon to Catechumens on the Creed [6, 14]
Our Lord Jesus Christ. . . is the Head of the Church. The Body belonging to this Head is the Church: not the local Church here, but both the local Church and the Church throughout the whole world; not the Church which belongs to the present time, but that which exists from the time of Abel himself even to all those who will ever be born, even to the end, and who will believe in Christ, the whole population of the saints who belong to but one city, which city is the Body of Christ, and of which Body Christ is the Head.” –Explanations of the Psalms [90, 2, 1]
Gennadius of Massilia (Died 496 A.D.)
“There is only one baptism, and it is found in the Church where there is one faith and where baptism is conferred in the name of the Father and of the Son and of the Holy Spirit. Therefore if those whom the heretics baptize by invoking the name of the Trinity come to us, they are certainly to be received as people who have been baptized so that the invocation and profession of the holy Trinity not be rendered useless. However, they are to be fully taught and instructed as to the Church’s understanding of the mystery of the Trinity.” –Ecclesiastical Dogmas Lu. Worship in the Early Church, An Anthology of Historical Sources, Volumes 1-4. Lawrence J. Johnson. Liturgical Press Collegeville, Minnesota
Pope Hormisdas (Died 523 A.D.)
“Following, as we have said before, the Apostolic See in all things and proclaiming all its decisions, we endorse and approve all the letters which Pope St Leo wrote concerning the Christian religion. And so I hope I may deserve to be associated with you in the one communion which the Apostolic See proclaims, in which the whole, true, and perfect security of the Christian religion resides. I promise that from now on those who are separated from the communion of the Catholic Church, that is, who are not in agreement with the Apostolic See, will not have their names read during the sacred mysteries.” -“Libellus professionis fidei” added to the epistle “Inter ea quae” to the bishops of Spain, April 2, 518; Denzinger, H., & Rahner, K. (Eds.). (1954). The sources of Catholic dogma. (R. J. Deferrari, Trans.) (p. 73). St. Louis, MO: B. Herder Book Co.
Pope Gregory the Great (540-604 A.D.)
“The Church is one, because it is founded upon the one Rock, which is Christ.” –Morals on the Book of Job, 1:27
Maximus the Confessor (580-662 A.D.)
“We are to accept the reverent meaning of dogma drawn from the expressions of the holy Fathers—and any other expressions we may find—that indicate unity as in no way contradictory of other statements of the holy Fathers that indicate duality. We know that the latter are mighty for the difference and against confusion, and the former are steadfast for the union and against division, but both, the former and the latter, we welcome exceeding gladly with soul and voice, as we confess the orthodox faith. And we wisely turn away those expressions that seem somehow contrary, the meanings of which are equally opposed to themselves and to one another and to the truth, and we boldly expel them from our home, that is from the Catholic and Apostolic Church of God.” -Opuscule 7. Louth, Andrew. Maximus the Confessor. The Early Church Fathers Series. London: Routledge, 1996.
Non-Catholic Quotes:
John Calvin
“It is to be numbered among the evils of our day, that the churches are so divided one from another, that there is scarcely any friendly intercourse strengthened between us; much less does that holv communion of the members of Christ flourish, which all profess with the mouth, but few sincerely regard in the heart.
Thus it comes to pass, that the members being divided, the body of the church lies disabled. Respecting myself, if it should appear that I could render any service, I should with pleasure cross ten seas, if neces-sary, to accomplish that obiect.” -Letter XVII: Calvin To Cranmer, Archbishop Of Canterbury, Wishes Health; in Théodore de Bèze, The Life of John Calvin. Translated by Francis Sibson (Philadelphia,
PA: Wm. S. Martin, Printer, 1836), 297-298.