In a world that seems more divided than it has been for decades – think Brexit, the Scottish independence referendum and Donald Trump, aside from the wars that have created millions of refugees – Steve Clifford says he was 'ambushed' by Jesus' teaching on unity.

The general director of the Evangelical Alliance has written his first book, ONE: Unity – a personal journey (Lion, £9.99). It's as though he didn't have a choice, he tells Christian Today. After a summer holiday last year he came back with a deep conviction that God was calling him to write the book, no matter how tough the timetable might be.

John 17, he says, is a chapter he hasn't been able to get away from during the eight years he's worked for the EA. 'I've lived in that prayer and every time I go to it there's something new in it. The prayer gives us an insight into the Father-Son relationship of the godhead, and we are drawn into that relationship – but it doesn't stop there, it's 'that the world might believe'.

And, he says: 'It's not just my agenda, it's something God is saying to the Church at this moment in time. There are frailties and struggles we're grappling with, but there are extraordinary signs of unity.'

Clifford found himself unexpectedly at the helm of the EA after the departure of his predecessor Joel Edwards – unexpectedly, because he came from the 'New Church' stream that had had little to do with traditional church structures. But as he tells the story in his book, this may have been an advantage. It's not just the world that's divided but the Church, the evangelical wing of it not least, and he spent the first months of his tenure meeting people, getting to know them and building relationships. And it's this emphasis on relationship that's key to how he's approached the theme of unity in his book. It's not about structures or institutions, but about family.

John 17 again: 'My starting point is, we get to call [God] father. As we look across the room, whatever differences in gender, class, ethnicity we see – yes, we're different, but we see brothers and sisters in Christ. We are family. Over the years, it's easy to get caught up into institutions. I want to put a flag out there and say Church isn't a business, it's about family.'

One of his priorities at the EA has been helping create gatherings of evangelical leaders where they can meet each other face to face. He discerns a 'unity movement' of Christian leaders – not just church leaders but people of influence in different fields – coming together and asking questions about what God is saying to them about their own towns and cities. A Movement Day is planned for London in October aiming to bring some of them together to share their visions and experience.

Face-to-face relationships, he believes, are key – though challenging. In his book he reflects on the story of an international gathering of evangelical leaders at which they shared what God was doing in their nations. A South American delegation rejoiced that one of them had won a beauty contest; a European walked out in protest at the objectification of women. They were later found drinking beer and smoking, actions equally shocking to those they'd criticised.

Clifford asks what we do when things go wrong, drawing on Paul's teaching about meat offered to idols in 1 Corinthians 8-10. We're to respect each others' consciences and be wise about when and where we raise objections – advice that, as a confirmed egalitarian in terms of women's ministry, he has to take on board himself when he's with those who hold a different view.

However, he admits: 'There's a danger we don't talk about stuff when it's too difficult -– there's a danger we shove it under the carpet.'

But there have been times, he says, when evangelicals have 'rushed to talk through deep theological differences, without the foundation of mutual respect'. This is one of the reasons he's made it a priority to bring evangelicals from different 'tribes' together – not just theological tribes, but across ethnic and generational divides too. His book has chapters about both of these – however much meeting in groups of young people or the same ethnic identity might provide mission opportunities, these 'homogenous' groups are 'not the finishing point' for the Church. And unity across racial divides has been particularly challenging, though at a personal level building wider relationships has been an 'absolute delight'.

'Ultimately, eschatology takes us to a place where we read in Revelation that people of all tribes, nations and language groups are before the throne,' Clifford says. 'The challenge for us is how we pull the future into the present. When a church has old and young, it's a reflection of the diversity of the community – we've got to work towards that snapshot.'

Toward the end of the book – the groundwork having been laid – Clifford writes of the hard question for all church leaders today, homosexuality and same-sex marriage. He has personal experience of how bruising such debates can be; not long after he took over as EA general director a storm broke around him when Steve Chalke, founder of Oasis, declared himself to be 'affirming' of same-sex relationships; a fraught debate followed which later saw Oasis asked to resign its membership of the EA. Clifford's account in the book is an important insight into how it played out from the EA's point of view, but he admits it was 'extremely difficult' and reflected a 'very painful time'. He stresses to Christian Today that he isn't saying they got it right 'every step of the way', but still thinks the resolution was the right one.

In his book, he reflects on what might happen in the Church of England if it agrees to some form of compromise over same-sex marriage as it did over women bishops. There is a 'high level of theological agreement' among evangelicals (which he shares) that same-sex marriage is wrong. Some would choose to leave, others to form links with different Anglican bodies. For others, he says, 'their premise is a strong desire to stay. The concept of the faithful "remnant" remains, and they possess a deep sense of loyalty to the institution that has been their spiritual home.' He sets this section in the context of a look back at the famous conflict between John Stott and Martyn Lloyd-Jones in 1966, where the latter urged evangelicals to leave 'mixed' denominations and the former urged them to stay. His own heart – though he doesn't say so outright – is clearly with Stott.

Unity is a difficult word. We'd all pay lip-service to it as a wonderful ideal. But it has to be fought for against the natural human tendency to divide. We also need to decide what unity looks like when differences are deep and genuine. What Clifford brings to the table is a passionate believe that we really are brothers and sisters in Christ, and that meeting each other face to face is the best way to realise this – and he's putting this conviction into practice by building relationships wherever he can.

So, he says: 'There are enormous challenges – but I think this unity thing that's happening is a reflection of what God's doing amongst us, and I think that bodes well for the future.'

ONE: Unity – a personal journey is published by Lion in April.  

Follow Mark Woods on Twitter: @RevMarkWoods