It's well known that the Church nationally is haemorrhaging children and young people – there will be an estimated 1.1 million fewer under-15s in church in 2020 than there were in 1990, according to Christian Research.

Arguably, then, the appointment by the Evangelical Alliance of a youth specialist to serve as its director of mission in succession to Dr Krish Kandiah is significant. Gavin Calver comes to the role from 13 years serving with Youth For Christ (YFC), for six years as its national director. He follows in a family tradition: his father Clive worked for both organisations and his grandfather Gilbert Kirby was also EA's general director.

Decline – across all age-groups – is not the only problem facing the Church in this country, however, and evangelicals face particular issues. One is how they are perceived by society at large – a US-based study for Mars Hill Church which resonates on this side of the Atlantic found that top of the list of reasons why people don't go to church are intolerance and social conservatism. Another is the fractures within the evangelical movement itself, particularly over the issue of human sexuality, which leads some to question whether the term is a useful one any longer – and whether the EA can act as a unifying force for all those who want to claim the title.

For Calver, his experience in youth ministry is a plus, but he points out to Christian Today that much of his work is with adults as well. "I think I do bring a more youthful edge and understanding – but culture is culture," he says. "When my Mum went on Facebook, I thought, should I come off it – but culture crosses generations."

He brings to his new role, he believes, "an understanding of culture, which in youth ministry is usually more sharp than it is in adult ministry" and talks of the need to find "ways of reinventing style, not substance".

One of the things that concerns him is that while the Church has "a greater reach than at any time I've been in ministry", through its work with Street Pastors, foodbanks and other social projects, it doesn't always put words and deeds together. "Every church has to ask itself, are we doing enough in word and deed? Some churches in this country are all word and no deed. But many more are great at deeds, but have to integrate word as well.

"The Church's reach is very wide, but if we're doing things that make us popular, we have to declare whose we are within that."

Is evangelicalism still a useful term? "If its just a label, it's not useful," he says. "If it stands for something more than a label, it's very useful. 'Evangelical' is potentially the table around which many of us can gather, and I certainly wouldn't want to be throwing out a word because it's misused. If it's misused, lets's redeem it."

He accepts, though, that the days of mass-movement evangelistic campaigns which characterised the work of evangelists like Billy Graham are probably not coming back. Evangelism today, he says, is "more relational – and it might be harder, but it's more likely to last.

"There needs to be a sense of journeying with others. I don't look back and say, 'I long to see stadiums full of people coming to faith.' That was for that day and if it happens again, great. But you can get people to put their hands in the air for anything. We want to see a nation of disciples."

In the face of the challenges facing the Church, he says, "The future has got to be reimagined. I don't believe the best days of the Church are behind it."

According to Calver, the average youth worker in a church lasts for about 18 months, while the average pastor lasts for between seven and 10 years. "Anecdotally, the reason for that is that youth culture changes every 18 months, but in adult culture you can get away with it changing every 5 to 10 years. The hardest, most tiring thing is to reimagine the style, so it fits with the culture of the world you're involved in. We need to hold on to the substance of the message that belongs to God, and reimagine the style a bit more."

It's just this separation between style and substance, though, that has proved so very difficult for evangelicals to handle, with strong sub-cultures emerging in which creationism, opposition to same-sex relationships and complementarianism – the view that men and women have different biblically-warranted roles – are all accepted as articles of faith. Calver would not be drawn on his own positions, but said: "I believe the EA should gather people around that which is primary, and accept people can have different views about that which is secondary. For me, the son of God became the son of man so the sons and daughters of men should become the sons and daughters of God. We've got to be together on what's totally primary. We can't go denying the resurrection. But I want to be part of an EA that's more defined by what it's for than by what it's against.

"I think that for too long evangelicals have been pigeonholed, and they spend their whole time on the back foot. All you do it, at best, answer the question till the next one comes along. I think it's time we started asking some questions of culture. We should be defined by what we're for. I'm pro-Jesus. I want to be pro the relationship: for too long we've been pro the rules."

Evangelicals, and the EA – like all Christians – still face enormous challenges, however. How far can you go in adapting to the culture without selling the gospel short? What counts as style, and what counts as substance? Is there enough evangelical unity left for the evangelicalism of which the EA is such a powerful symbol to be a coherent and positive force for mission in the 21st century?

Gavin Calver is one of two new – and youthful – appointments at the EA. Both of them will take up roles that will bring them face to face with big questions and no easy answers.