I’m in the serenity of Martin Hall, in Edinburgh’s New College on the Mound. The religious scholar and public intellectual, Mona Siddiqui, is talking to the singer-songwriter and broadcaster, Ricky Ross. The early evening sun is streaming in and Ricky has regaled us with words and music. It’s all rather sublime.

And then, towards the end of the conversation, Mona asks Ricky whether his faith is a place of contentment. Ricky is a practising Catholic, who doesn’t shy away from acknowledging his faith. He plays gently with the question. Not really, he concludes, it’s more a place of restlessness. Without hesitation, Mona concurs. Faith should be restless, she says.

Eureka. For me too, the resonance is immediate. I’ve been wrestling with the tension between contentment and restlessness for decades, more often than not in the midst of a public discourse which made that seem somehow wrong. When did that battle begin for me, I wondered, as I slipped away that evening? The answer was closer to hand than I thought, albeit a long time ago.

It’s the summer of 1978. I’m17. It’s the middle of the night and I’m lying in a sleeping bag on a camp bed in the aisle of a church in Nefyn, a small village on the coast of the Llyn Peninsula in North Wales. I’m one of the male workers on the CSSM, the Children’s Special Seaside Mission. Everyone else is asleep but I’m wide awake. It’s partly the heat but something else is happening too.

We’ve spent our summer holidays in Nefyn for a few years now. Normally a couple of weeks, either camping or in a cottage given over to lettings for the summer season by local residents. And taking part in the CSSM has become part of the holiday. It’s run by the evangelical Scripture Union, over a three week period in August each year.

The clue’s in the title. It’s a mission and its purpose is to spread the word. Specifically to children, aged five to sixteen. To teach us to be good Christians. The youngest are Shrimps. Then there are the Mini-Sprats, the Maxi-Sprats, the Sharks and for 14-16-year-olds, the Holiday Club.

The enterprise is run from, Pendorlan, a large rambling semi-detached house not far from the cliff top high above the beach which runs the course of Nefyn’s sweeping bay facing out to the Irish Sea. The female mission workers stay in the house but it’s not big enough to accommodate the men which is why we camp out in the church.

There are daily activities, morning, afternoon and for the older children, early evening too. A lot of it is just pure fun, much of it down on the beach if the weather is fine. A tug of war or a game of rounders on the sands. But some of it is more serious, centred on Bible reading. For the Holiday Club, in particular, talking about Jesus is part of the deal.

The workers are volunteers, led by Peter, from East London, who is there with his wife Wendy and their children. The rest are a ragbag assortment of disciples, mostly younger folk, students and the like. A rather earnest bunch with a hint of drabness. But then, it was the 70s so I guess that covered all of us. And anyway their sincerity was beyond question.

Peter is a kind man with a wide grin and an infectious enthusiasm for life. He’s one of the good guys. He seamlessly combines accepting you just as you are, warts and all, with a deeply held conviction that your life will be enriched if you let Jesus into it. He’s a man on a mission.

At seventeen, I’ve made the transition from Holiday Club member to worker, a rite of passage of sorts. I’m a serious, bookish sort of teenager too. I’ve been going to church all my life and back at home I’m involved in the Pilots, the church youth club. So it’s all rather inevitable and obvious. My group for the week are Mini-Sprats, seven to nine-year-olds, mostly on holiday in Nefyn, just like me.

But I’m a grown up now, and as a mission worker, I’m not Chris but Mr Eades (my previous surname). A tad pompous but I suppose in its own way it helped to create boundaries and a sense of responsibility on our part as workers. And although it was partly about playing games, our core task, was simple. To help lead the children to Jesus.

That much I know. But now, in the quiet of the warm night, I’m restless, unnerved. It definitely has something to do with the religious imagery looming around in the long shadows of the church interior. Probably not the best place to experience a crisis of faith when you’re still just a callow youth.

And yet that is what’s happening. For the first time in my life, I’m wrestling with my belief in God. It, like me, is in an unfamiliar place. Perhaps, looking back, my journey to that moment had been one of blind faith. But that feels too harsh a judgement. I think it was more a case of gentle naivety, not so much the lack of a willingness to question but more the lack of a need.

Sure, we’d had our moments at home. Most notably when I’d joined a running club which wanted me to train on Sunday mornings. That meant missing church. My mother wasn’t happy and we’d even had the Minister round to the house to talk it through. But we’d hammered out a compromise. My faith wasn’t in question, just the obligatory institutional transaction that came with it.

Trickier had been my first skirmish with the fear of the grim reaper. I’d invited the Minister’s son, an even more serious teenager than me, round to talk about it. It wasn’t just a fear of mortality in a literal sense, but something too about the meaning of it all. Was God the problem, or part of the solution? We talked our way around that soberly and for the most part, my mind was gradually put at ease.

This moment, though, was different. Not just a brush with doubt in faith's lowlands but a fracas somewhere much closer to the summit. Now, in the dark lonely night, I felt like I was in freefall. Yet what had precipitated this wrestling was nothing more evening prayers in the garage at Pendorlan. Crammed into the dusty, windowless space, we had prayed for the mission.

Led by Peter, we were encouraged to feel God in our midst. Strongly encouraged, implored even. The peer pressure to feel God's presence rippled around like a lightning rod. Yet I just couldn’t feel anything at all. Except hot and bothered. After all, we were in a garage sitting on an odd assortment of chairs from the house. It was all terribly earthly and for me, at any rate, God just wasn’t there or at least not in the way that everyone else appeared to be experiencing.

It wasn’t just that it seemed a bit absurd. It felt alien and suffocating. Even though we were technically Catholics, my mother’s fall out with Catholicism meant that I had grown up largely with the stripped back bareness of Congregationalism. There was no question that God was there, but nobody felt the need to dwell on it. This new experience wasn’t even akin to the heavy ritual of Catholicism either, which at least would have been familiar. Christianity had always been intuitive. Now, suddenly, I didn't know what I believed anymore.

Until that evening the mission's Evangelicalism, in so far as I was aware of it at all, had been benign. But there in the garage, I could no longer suspend disbelief. Something had changed. For the first seventeen years of my life, faith had been a place of contentment. It had wrapped me with reassurance. What a friend we have in Jesus, wasn’t just a hymn, it was a way of being in the world. But now I had a new friend called doubt. I didn’t know it then but doubt hadn’t just dropped by for a chat. It had come to stay for a lifetime. Faith's restless journey was only just beginning.