In our day, there has been a revival of discussion surrounding church membership and other aspects of church polity. But are these matters simply modern inventions? How did the early church think about these matters?
Writing in the 2nd century AD, Irenaeus bishop of Lyons combated the Gnosticism of his day in his most famous work, Against the Heresies. Throughout his work, he appeals to sound reasons and the Scriptures to combat the Gnostic teachings of Valentinus, Marcion, and other heretics. However, Irenaeus shows himself to be not only a theologian but also a devoted churchman. One prominent theme throughout this work is how all the churches scattered throughout the world possess the tradition of the apostles and “preserve the same form of ecclesiastical constitution.”  There is a visible unity of church order which characterizes all the churches. In saying this, Irenaeus does not lay out an explicit church polity. Rather, he describes in general terms the practice of the churches, and these practices serve to make the point that the church is indeed built on the Gospel. In putting those pieces together, it becomes clear that this structure is a significant apologetic against the Gnostics, creating a clear separation between the world and the church.
The Anti-Institutional Views of the Gnostics
Though the Gnostics resented being excommunicated from the church, they were not able to create an organized counter-movement of their own. J.N.D. Kelly writes, “To speak of Gnosticism as a movement is misleading, for that term suggests a concrete organization or church. There were, as we have seen, plenty of Gnostic teachers, each with his coterie of adherents, but there was no single Gnostic Church.” This is not to say that there was no structure to the Gnostic gatherings at all. In many ways, a Gnostic gathering would have looked not much different from a Christian gathering with adherents gathering around a teacher, studying their scriptures, and performing their rites.
However, Gnostic teaching fundamentally looked down on the idea of an institution. Even while the Gnostics maintained their own gatherings, they understood themselves to be above those gatherings and not subject to them in any way. They would disparage those belonging to the church as “vulgar” and “ecclesiastic,” because they remained trapped in their institutional ways of thinking and living.
The “Ecclesiastical Constitution” of the Church
Irenaeus, on the other hand, would not apologize for the “ecclesiastical constitution” of the church. Rather, he understood the institution of the church to be the very thing which defends and displays the power of the Gospel.
The church is to be composed of those who retain unchangeable in their hearts “the rule of the truth which [they] received by means of baptism.” From the time of the apostles, baptism was the initiatory rite into fellowship with the church. This means that in some way, whether through public confession or catechesis or some other means, Irenaeus takes it for granted that every member of the church has received “the rule of truth,” that body of apostolic teaching which proclaims the Gospel. Those who do not hold fast to “that well-compacted faith which they received at first through the church” will be exposed to God’s judgment.
In discussing baptism, Irenaeus assumes the concept of membership in the church, that a Christian is baptized into a local body of believers. Whatever practical form this membership took, whether signing official documents or public confession, Irenaeus understood that the church had to have some way of expressing who belonged to the church and who did not, who confessed the apostolic faith and who did not. Irenaeus speaks of those who are cleansed from demons and “believe [in Christ], and join themselves to the Church.” True faith in Christ will lead to identifying with Christ’s people. This is why Irenaeus can say that those “who do not join themselves to the Church…defraud themselves of life.”
But membership in the church is no passive thing. Rather in the church, we see God’s Spirit at work through the lives of God’s people. Irenaeus’ description of the activity of the church is nothing short of supernatural. Within the church, we see the prophetic gifts manifested, sight restored to the blind, the lame cured, the body healed, demons cast out, and even the dead raised. For Irenaeus, these works do not so much confirm the power of those who perform them, but rather they give proof to the fact that Christ dwells in the church, as these are His works that are being accomplished in the church. None of the Gnostics can claim such a validation from Christ.
Additionally, and perhaps more significantly, the members of the church are characterized by holiness, demonstrated in acts of mercy and generosity, “for as she has received freely from God, freely also does she minister [to others].”
but in the Church, sympathy, and compassion, and steadfastness, and truth, for the aid and encouragement of mankind, are not only displayed without fee or reward, but we ourselves lay out for the benefit of others our own means.
Far from the slavish mentality of the ancient Jews who gave only a tithe, Christians now in their freedom “set aside all their possessions for the Lord’s purposes, bestowing joyfully and freely not the less valuable portions of their property, since they have the hope of better things [hereafter]; as that poor widow acted who cast all her living into the treasury of God.” Again, here we see the unity of the churches, not only in doctrine and church structure but also in the morality of her members. In contrast, Irenaeus points out the corruption and wickedness of the Gnostics, using their freedom for their selfish pleasures and gain, rather than for the good of others. The holiness of the members of the church commended the truth of the gospel, while the wickedness of the Gnostics revealed the depravity of their beliefs.
Suffering & Perseverance
Perhaps the greatest evidence of the supernatural life within the church is in her “multitude of martyrs.” Unlike the Gnostics, who cannot point to any such witness, “the Church alone sustains with purity the reproach of those who suffer persecution for righteousness’ sake, and endure all sorts of punishments, and are put to death because of the love which they bear to God, and their confession of His Son.” To be a part of the church is no light thing, but can cost one even his life. Those who belong to the church are those who persevere in faith, even to the end. Through them, the truth and power of the Gospel are displayed.
Despite the church’s best efforts to discern a genuine profession of faith, there will be instances where professing believers fall away from the faith. In those instances, Irenaeus assumes that churches will not stand by silently, but will take action to remove those people from the membership of the church.
But as many as separate from the Church, and give heed to such old wives’ fables as these, are truly self-condemned; and these men Paul commands us, “after a first and second admonition, to avoid.”
To accept the false teaching of those outside the church is, in effect, to separate oneself from her. And the church is to make this separation explicit, first by warning the person, then by an act of discipline. This is to apply not only to her members, but even her leaders and teachers belong to the church only insofar as they hold on to the Rule of Truth, which they confessed at their baptism. Here, the ground of all fellowship with the church is made clear: a credible profession of faith in the Lord Jesus Christ. For all those who fail to hold on to that truth, they also are to be put outside the fellowship of the church.
Yet this act of discipline is not to be done for their destruction, but restoration. Irenaeus tells one account of the wife of a deacon who was taken in by a false teacher.
A sad example of this occurred in the case of a certain Asiatic, one of our deacons, who had received him (Marcus) into his house. His wife, a woman of remarkable beauty, fell a victim both in mind and body to this magician, and, for a long time, traveled about with him. At last, when, with no small difficulty, the brethren had converted her, she spent her whole time in the exercise of public confession, weeping over and lamenting the defilement which she had received from this magician.
Though once belonging to the church as the wife of a church officer, she separates herself from the church, only to be abused by the magician. But the church does not abandon her. Rather, “with no small difficulty” the church family pursues her and wins her back to the faith. Through “the exercise of public confession,” demonstrating her genuine repentance, she is received back into the church.
This restoration is the purpose for which Irenaeus has written this work, not merely to condemn the heretics, but to call them back to the one true faith. As those who perhaps at one point belonged to the church, but now have abandoned her, Irenaeus is now pursuing them with the truth of the Gospel. He prays “that they, being converted to the Church of God, may be lawfully begotten, and that Christ may be formed in them, and that they may know the Framer and Maker of this universe, the only true God and Lord of all.” To win a false teacher to the Gospel is to convert them to the church, where the true knowledge of God rests.
Far from being merely “vulgar” and “ecclesiastic,” Irenaeus understood that the right practice of the church as handed down by the apostles preserves and embodies the truth of the Gospel. The church is the “pillar and foundation of the Truth.”
Irenaeus knew that his battle against the Gnostics could not be limited merely to his force of reason and his writings. Rather, just as important as exposing their false teachings and explaining the Scriptures was the need to maintain a right ordering of the church. To win debates at an intellectual level, but to neglect the church would only result in sure defeat over time. But by maintaining a right understanding of the church, he would ensure the preservation of the Gospel for ages to come.
In preserving the church according to apostolic teaching, she becomes a garden like the Garden of Eden. Irenaeus writes,
For the Church has been planted as a garden (paradisus) in this world; therefore says the Spirit of God, “Thou mayest freely eat from every tree of the garden,” that is, Eat ye from every Scripture of the Lord; but ye shall not eat with an uplifted mind, nor touch any heretical discord. 
In the church, we may feast freely from the Scriptures, being grounded in the tradition of the apostles. Though we live in a world filled with the poisons of every kind of false teaching, in the true church we find a paradise garden where the Gospel is proclaimed and the Spirit of life reigns.
 Ante-Nicene Fathers, vol. 1, The Apostolic Fathers, Justin Martyr, Irenaeus, eds. Alexander Roberts and James Donaldson (Peabody: Hendrickson Publishers, 2004), 315-567. Hereafter, I will be citing the text of Irenaeus’ Against the Heresies by book, chapter, and paragraph. AH 5.20.1.
 Kelly, Early Christian Doctrines, 26.
 Behr, The Way to Nicaea, 42.
 AH 3.15.2.
 AH 1.9.4.
 McKinion, Life and Practice in the Early Church, 5.
 AH 1.13.4.
 AH 2.32.4.
 AH 3.24.1.
 AH 5.6.1.
 AH 2.31.2, 2.32.4.
 AH 2.32.4.
 AH 2.31.3.
 AH 4.18.2.
 Roch A. Kereszty, “The Unity of the Church in the Theology of Irenaeus,” in The Second Century, 4 no. 4 (Winter 1984), 206.
 AH 2.32.1-2.
 AH 4.33.9.
 AH 1.16.3.
 AH 1.13.5.
 AH 3.25.7.
 AH 5.20.2.