David Kinnaman is arguably the world's expert on the faith of millennials; those born after 1984 and before 1997. David was so interested in the question of what we can learn from this age group that he bought the Barna Group – a polling and research firm for Churches – while still in his twenties.

I have known David for eight years now and have consistenly found his insights on how the Church is going to disciple and reach the rising generation profound. I asked him why he became interested in researching how millennials think.

"I am super-interested in people's faith journeys – conversion and de-conversion," he told me.

"Actually the process of de-converting is as powerful a faith journey as conversion. We assume people have walked away or put their faith on the shelf for a simple set of selfish reasons, but they have a lot of personal identity and really specific reasons for doing it. Going back to my high school years I had a couple of friends who had come to faith and committed themselves to Christ and then really become spiritual nomads, less interested in spirituality. So there's a personal narrative to my interest and I was interested in using research as a way to understand that."

I first came across David through his bestselling collaboration with Gabe Lyons, UnChristian: what a new generation really thinks about Christianity. The book documented that the dominant perceptions of Christianity held by 16-29-year-olds in the United States came out as anti-homosexual (91 per cent), judgmental (87 per cent) and hypocritical (85 per cent).

These were damning results and struck fear into those seeking to evangelise the millennial generation. Before you even start to explain the gospel there is a pre-loaded prejudice and negative stereotyping attached to Christianity in the USA. But eight years on, I asked David if these were still the dominant perceptions among that age group.

"They are definitely still part of it. In a new book Gabe Lyons and I have coming out in 2016 the research shows that now the perception is Christianity is irrelevant and so people are consequently indifferent that Christianity has any kind of moral truth claim," he said.

"They don't believe that Christianity has made the world a better place, they think its quite the opposite, which contributes to the second perception which is they think we are extremist. So society perceives Christianity as irrelevant and extreme."

This is not great news, but Christianity in the West needs to hear these findings and quickly. The public relations team at Volkswagen cannot ignore the impact that the emissions rigging fiasco has had on the car manufacturer's hitherto rock-solid reputation; we who seek to commend the Christian faith need to be clear on the perceptions of Christianity in the wider culture.

But, I asked Kinnaman, is the solution for Christians to try to appear more relevant and less extreme? He thinks this would be a mistake.

He explained: "There's a real powerful movement towards the centre where the idea is that if we could just sand off all the extremist edges then we could all live as one happy family. But the notion of being extreme in a lot of other ways culturally is actually a really good thing.

"For example exercise is an extreme stress you put on the body. Extreme sports, extreme makeover – and it is usually a good idea. So sometimes it is in the extreme that we are made stronger."

He is of course aware that there is a dark side to extremism in "terrorism and a theocracy". But Kinnaman wants to warn the Church about compromising its beliefs in order to become more socially acceptable, and he also has some encouraging advice to a church wanting to engage young adults: "Millennials are a group of people that are going to lead the church to a new place. Not on their own but with us the older generation."

He speaks about how the biblical character Daniel and his peers in exile offer us a way of understanding millennials in the Church. "Although not every generation is in exile, this generation of millennials is learning how to be faithful in a foreign land. We call it 'Digital Babylon'. For that reason we need exiles; they are not incidental, they are integral to the purpose of God during times of great social change," he said.

"I actually think millennials are very important for the church to incorporate and to allow them to lead us into faithfulness to God in a new context."

I like Kinnaman's positive vision for the way that a generation of young adults could hold important clues as to how the Church remains faithful to her mission in changing times. But he is clear that this age group are not the hope of the world.

"Millenials are not perfect, they are not our salvific hope: Jesus is and always will be," he says. "But they are bringing a new fresh orientation to what it is we believe and why we believe it."