The word “catholic” comes from the Greek expression kath’ holon or “in accordance with the whole.” As applied to Christian belief and practice, its basic meaning is “holistic,” “comprehensive,” or “well rounded.” The classic definition of catholic faith came from Vincent of Lérins around AD 434:
Moreover, in the catholic Church itself, all possible care must be taken that we hold that faith that has been believed everywhere, always, by all. For that is truly and in the strictest sense “catholic,” which, as the name itself and the reason of the thing declare, comprehends all universally. We shall observe this rule if we follow universality, antiquity, consent. We shall follow universality if we confess that one faith to be true which the whole Church throughout the world confesses. We shall follow antiquity if we in no wise depart from those interpretations which it is manifest were notoriously held by our holy ancestors and fathers. We shall follow consent, in like manner, if in antiquity itself we adhere to the consensual definitions and determinations of all, or at the least of almost all bishops and teachers. (Commonitory 2)
In short, to be “catholic” is to be in harmony with what has been believed always, everywhere, and by all. You don’t have to be “Roman Catholic” to be catholic. Luther, Calvin, Wesley, and in fact most of the great Protestant thinkers frequently appealed to the ancient Fathers of the church as justification for their views. The Reformers’ grievances against Rome, as they saw them, grew out of Roman deviation from catholicity. In a word, it wasn’t that the pope was “too catholic,” but that he was “too Roman”; he was “not catholic enough”!
“Mere” catholicity builds upon C. S. Lewis’ description of “mere Christianity,” the bare and essential minimum of Christian faith. Lewis imagines Christianity as a vast building, in which “mere” Christianity
… is more like a hall out of which doors open into several rooms. If I can bring anyone into that hall I shall have done what I attempted. But it is in the rooms, not in the hall, that there are fires and chairs and meals; even in the hall, you must begin trying to obey the rules which are common to the whole house. And above all you must be asking which door is the true one; not which pleases you best by its paint and paneling. In plain language, the question should never be: “Do I like that kind of service?” but “Are these doctrines true: Is holiness here? Does my conscience move me towards this? Is my reluctance to knock at this door due to my pride, or my mere taste, or my personal dislike of this particular door-keeper?” (Mere Christianity, Preface)
This analogy of a house with many rooms fit well with Lewis’ era. In our post-denominational age, however, the situation is far more complicated. We discover that there are often partitions between some of the rooms, and that more and more Christians are freely moving back and forth between them. Meanwhile, others are undertaking to tear down some of the walls entirely. Others (perhaps the majority) still prefer their chosen rooms, but they find their faith is deeply enriched by occasional visits with those who have chosen differently.
Many qualifiers can get attached to catholicity. There are Roman Catholics, of course, and the Orthodox refer to themselves as catholic as well. The churches of the Union of Utrecht, along with scores of smaller jurisdictions, comprise a highly diverse “independent catholic” movement. Some Lutherans call themselves “evangelical catholics.” The Church of England is “reformed catholic.” A. T. DeGroot has even suggested that Disciples are “free church catholics.” The core content that makes any these groups catholic (if indeed they are) is what comprises “mere” catholicity. This content is not the “lowest common denominator,” but rather the highest and most central expression of Christianity. If there is any hope for genuine Christian unity, it will be through the recovery of “mere” catholicity.
If Lewis could describe “mere Christianity” as a kind of foyer through which all Christians pass before settling into a room, I would suggest that “mere catholicity” is rather a kind of “community meeting place” where Christians can bring their particular treasures and share them with the greater Church. It is “catholic” in that there are ground rules for this sharing. The treasures we want to share are those that harmonize with rather than overturn the deposit of faith we have received: the faith of classic Christianity. It is “mere” because it does not presume the superiority of any particular denominational (or non-denominational) structure, ethos, or theological system. We share what we can, where we can. But at the end of the day we expect to return to our customary places of worship and service, hopefully transforming them from the inside through what we have experienced.
In a nutshell, “mere” catholicity is what happens when Christians of whatever ecclesiastical tradition seek to be informed by the ancient church in its doctrine, ministry, discipleship, and worship. It is radical in that it seeks to get back to the root (Latin radix) of the matter: the faith and practice of the apostles and those who first lived by the apostles’ teaching. It is a leaf that knows it is part of a tree, and holds no illusions about its status in the greater sweep of Christian history. It does not assume that nothing of any practical or spiritual significance happened between the death of the apostles and the rise of the current generation of churches, parachurches, megachurches and TV evangelists.
“Mere” catholicity is convergent in that it finds itself at the confluence of three great streams of Christian tradition: the evangelical, the charismatic, and the sacramental. It believes the Holy Spirit is still at work in the world and that the church’s best days are still in the future. Therefore it admits that no one has a monopoly on the truth and confesses with John Robinson that “God hath yet more light and truth to break forth from the Word.” It seeks to bring the best of Christian wisdom to bear in personal spirituality and corporate worship, in the process creating a new thing that isn’t really new at all, but rather a fresh incarnation of what God has dreamed for the Church since the beginning.
“Mere” catholicity is ecumenical in that it seeks to live in unity with other Christians on the basis of St. Augustine’s dictum: “in essentials unity, in non-essentials diversity, in all things charity.” Here it must be noted that Vincent’s definition itself applies strictly only to matters of core Christian theology. He writes,
Yet in the investigation of this ancient consent of the holy Fathers we are to bestow our pains not on every minor question of the Divine Law, but only, at all events especially, where the Rule of Faith is concerned. (Commonitory 28)
Vincent also allows for the possibility that there be genuine progress in doctrine, and that elements once “latent” or “neglected” in earlier Church tradition might legitimately be strengthened or made explicit in the future (Commonitory 23). “Mere” catholicity must therefore be, in a sense, minimalistic. “Mere” catholics may have very deeply held biblical convictions about secondary matters such as the sacraments, women’s ordination, church governance, tongues, etc., but extend liberty to those who have come to differing conclusions within the bounds of classic orthodoxy, and a loving, non-coercive witness even to the most outrageous heretics.
In the late 16th century Lancelot Andrewes described the foundational approach to theology that characterizes Anglican catholicity in these memorable terms: “One canon, two Testaments, three creeds, four general councils, five centuries, and the series of fathers in that period determine the boundaries of our faith.” It is to this common deposit of faith that “mere” catholicity appeals.