Book Review: Unity and Diversity


This book review is a little strange, and may be a little long. It is of a book published thirty years ago, in a different context and conversation, but about such a timeless and timely topic that it jumped off the shelf at me whilst I was looking for something to read one sunny afternoon.

Oscar Cullman was a New Testament Scholar of the Lutheran tradition, who died in 1999. Well known for his ecumenical work, Cullmann also wrote on Eschatology (The End of the World) and Christology (Jesus), and that is the context I best know/had read him as an undergraduate. I was thus intrigued to know that he was also a serious ecumenicist – devoted to the study and practice of Church unity/relations. It is from these twin fields – The New Testament and study of the Church in the world today – that this book comes.

Readers may know that I am passionate about, but also quite specific about, unity. I’ve worked in a Anglican Mission Agency, for an Anglican Bishop, did my MA at an Anglican College, grown up in and loved a Baptist Church, served in and been part of a Vineyard Church, gone to an Anglican Church, worked at an inter-denominational theological college, spoken and listened at conferences in a range of countries and contexts, and worshipped and done mission alongside people from a range of traditions. I love the local church as a fingerprint of God’s kingdom on the ground, and long and pray for the ultimate unity of the global and historical Church as an answer to Jesus’ mighty prayer in John 17. I love seeing what God is doing globally and nationally through, for example, student mission movements like UCCF/IFES, united in the Gospel and with a vision for evangelism. None of these, and definitely not me, fully capture the heart of the Triune God who Scripture reveals, however, and I personally believe that church unity is something caught in the ‘now and the not yet’ of the kingdom of God.

I say this by way of introduction to partly give some context, and also partly to say just how important I found this book in articulating some of these thoughts. Cullman provides a model of doing theology in an ecumenical context/conversation that I find inspiring, challenging, and encouraging. I’m quite sure I couldn’t go as far as him in some things, but his desire to both see the unity of the church begin to form and remain committed to truth, is wonderful. Interestingly, this is because the book is both grounded in New Testament exegesis and written and articulated with an eye on the practical outworking. This book is neither a New Testament monograph – though Cullman can and has written many – nor an overly practical, biblically-disconnected ‘handbook’ (of which, in my opinion, far too many modern books are).

So what does he actually say?

Cullman writes a theologians book – he is careful throughout to define his terms and substantiate his argument. But he also writes as a disciple of Jesus – and this best comes out through his respect and warmth towards those with whom he firmly disagrees but who also claim the name of Jesus. By seeing the good in those who follow Christ in other flavours of the ecclesiological stew, to mangle a metaphor, Cullmann challenges us about what unity looks like, expressed through diversity.

With his New Testament background, Cullman’s argument is refreshingly biblical. He takes as a key motif the language of ‘charism’ (or ‘gifts’) around the Holy Spirit constituting the Church as the body of Christ. On the opening page comes his bold claim that;

Every Christian confession has a permanent spiritual gift, a charisma, which it should preserve, nurture, purify and deepen, and which should not be given up for the sake of homogenization

This is an important starting point. Every Christian confession/expression has something to offer. Though it should not need saying, implicit throughout Cullmans work (and often lacking in many public declarations of ‘unity’ in the political sphere, for example) is the importance of the Christian-ness of unity. It is shaped like Jesus because it is about, for, by, with, from, to and in Jesus. Secondly, this notion that actually, rather than the different streams of the Church being a ‘bad thing’, these are different expressions of God’s gifts, much like the different gifts of the Holy Spirit. This is a powerful place to start talking about unity from – recognising the differences, but at the same time seeing them as good, as gifts to be shared not as barriers to be broken. 

Unity through Diversity is a book woven through with the central place of the Holy Spirit – and this is something that is often overlooked or over-simplified in discussions and declarations of unity. Cullmann writes that ‘to create unity belongs to the essential nature of the Holy Spirit‘, echoing part of the Spirit’s Trinitarian role, and continued missional filling as history rushes towards God’s ends for it. Cullmann, with this pneumatological hat on, advocates a sort of radical middle between two equal and opposite errors surround talk of the Holy Spirit and Unity:

The denial of the work of the Holy Spirit has two opposite results, each of which is equally fateful for the cause of Christian unity: on the one side an anarchic ecumenicism, and on the other side its exact counterpart, a hardening of confessional barriers that excludes any hope for unity. Both attitudes – and they are both present in our activities these days – oppose the work of the Holy Spirit.


Cullmann doesn’t pull and punches here! He doesn’t name and shame, but recognises the reality of two different, opposite errors surround the role of the Holy Spirit with regards to the unity of the Church.

As a New Testament Scholar, Cullmann is rightly and carefully concerned with what is called ‘salvation history’, which I would (probably inaccurately) simplify as the story of Jesus with regard to his saving and renewing the world. This story, this history, is recorded in vital detail in the New Testament – with the birth and explosion of the Church. This is the story into which all Christians are called and infused. The way Cullmann writes of this is beautiful – recognising the normativity of the New Testament for us now, the fact that ‘there was no uniformity even in earliest Christianity‘, and that in fact the true unity of the Church is in part to do with its diversity:

A false ecumenicism which seeks merger confuses these two streams (unity and diversity). It considers the historical origin of the different confessions and the resulting variety as such to be resistance to God, as merely an example of human bungling. Its goal is that abstract construction of which we have spoken, an abstraction remote from all that has actually developed in history.

We ignore the past at our peril.

Towards the ending of his book, Cullmann offers the reader a tantalizing chapter, titled simple ‘The Actualization of Unity Through Diversity’. He reviews various technical agreements, theological discussions, and historic proclamations, but closes with an insightful quote. A prayer written for the 1935 Week of Prayer for Christian Unity; “Unity of the Church of Jesus Christ, how he wills it and when he wills it.” Cullmann closes his chapter; ‘Both are important. But at the end of this chapter I would especially like to emphasiz: “HOW he wants it.”‘. From here, the book moves into a posture of realistic hopefulness – the kind of thing I always enjoy when I realise I am reading something that whispers of and points towards the glorious Kingdom of God.

Given the European authorship of this book, and the reality that much historic disunity (in the Church sphere and beyond!) has been focused on the West, it is worth mentioning the way that Cullmann discusses one of the big questions at the heart of many conversations on Church Unity – what about Roman Catholicism? Cullmann is gracious and careful in his discussion, interacting winsomely with statements from Popes, Cardinals, Councils and theologians. Not least amongst these is Ratzinger, who would eventually become Pope himself, who is given real respect given the honesty and and reality of what he writes. Soberingly, however, Culmann’s general observation about unity in this context comes down in no small part to the Roman Catholic declaration/Doctrine of the Pope as gaurantor of Church unity, and the non-Roman Catholic rejection of this. Without wanting to jump sideways into a discussion of eschatology, there is a disjunction between official Roman Catholic teaching of the unity ‘now’ of the Church, compared with the fragmented reality of the ‘not yet’ we actually find ourselves in. Cullmann is careful to play the ball rather than the man, however, and his friendly disagreement with Ratzinger is a model in irenic discussion.

Regarding what this looks like, I give more space to Cullmann:

Nevertheless, a fundamental difference in fact separates the Catholic concept of the church from the Protestant: it concerns the tension between ‘already fulfilled’ and ‘not yet complete’ which I have argued is basic to the New Testament understanding of salvation history in my book ‘Salvation in History’ and even earlier in ‘Christ and Time’… 

He goes on, recognising the reality of different Doctrine, not disrespectfully but by way of recognition. His summary point, then, in this particular chapter (on the cusp of the close of the book), is wonderfully hopeful:

From my perspective I see a practically irreconcilable difference on this point, measured by human standards, and consider it to be an enormous obstacle obstructing ecumenical endeavors. But I believe that like the other difficulties it is not insurmountable if we hold to the plan developed in this book of a community of churches in which all churches, just as they are, can find their place.

This is an inspirational challenge. This is a challenging book. I would urge you to read it, even if it is from 30 years ago, if you are interested in or praying for the unity of the Church. There is nothing but God that can truly unite His Church – it is not something we can ‘do’. This book powerfully observes the danger of trusting in human leadership – whether that human be a Pope, Archbishop, or other leader – by drawing the reader back to Jesus and his Kingdom. I can’t say I agreed with every word of this book – and, of course, there are sections I simply didn’t understand – but overall this is a powerful bit of Kingdom-saturated theology that I would love to be more widely read and engaged with by readers and leaders as different churches grapple with the now and not yet Kingdom of God, and what that looks like as we think about unity now.

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