It isn't every day that you get a lift from the NYPD. In fact it isn't every year. But today I'm lost in Harlem and it's raining and no-one seems to be able to direct me to the the school where I'm meeting John and Greg from Young Life International.

But it's the NYPD to the rescue, taking pity on a lost English guy and giving him a lift about 10 blocks. It was quite an entrance. For once I was officially cool. It was one of those experiences that money can't buy.

Greg works at this school (and at other locations) as a mentor to the youngsters here and my time with him is pretty inspiring. What's more it's his manor – he grew up just round the corner from the school and his mum still lives here in this part of Harlem. This is his place and he cares about it.

First stop is a music class run. The teacher is a big man with a personality to match. He's also a believer and there's something of that faith that radiates though him and his lesson. As we enter the classroom youngsters show open affection for Greg and it's humbling to be here with them. They like him and trust him – that's clear.

A student is singing and as she finishes the teacher invites her fellow students to give some positive feedback – or glows. The atmosphere is positive. He then asks for some grows – ways of doing the piece a bit better. The kids are polite – perhaps having visitors is having an impact. But the teacher is having none of it. This youngster is great – she has more greatness within her. He wants to push her and release an even better performance.

'Come on I want you to imagine we are asleep, wake us up!'

The student tries again – much better.

'Try again, wake us up. Remember why this song is important to you!'

There is something profound in the idea of singing so you wake people up. In some ways, teachers with a faith are part of that great spiritual awakening that is at the heart of any personal conversion. What is becoming a follower of Jesus if it isn't waking up?

What is also profound is the school's commitment to the kids and wanting the best for them. And that's not something restricted to the US. Our schools here are packed with similar aspirations and commitment.

As we chat about the lesson, Greg has an insight. We are talking about singing and how it is a powerful way of affirming all that is good and precious about human life.

'Singing is important. What really inside a person always comes out when they sing. They can't hide it. They choose a song because the words mean a lot to them. When you get to talk to people they'll tell you about their lives and how a song goes deep to the heart of their problems and difficulties.'

How true. There is something Godly about singing and being a mentor with kids as they sing is a precious thing. It's a Godly calling and it's facilitated by Young Life International, which puts people like Greg into places that need blessing. Indeed, there are Young Life mentors like Greg in places of need in dozens of locations. It's inspiring and a testament to an initiative that is determined to be the change, not just to call for it.

This school is inclusive in the best way. It's in a tough neighbourhood and draws youngsters from all parts of the NY area. The sheer discipline of studying here adds a level of valuable life skill and resilience.

Many of the kids have difficult lives so having a mentor like Greg is a gift. Greg is there to walk besides people. Greg has made himself indispensable. He's on the school advisory board. He gets called in to be with kids and families when there are difficult issues to deal with. One of the students died recently and it was Greg who was called in to be with the bereaved family.

That's a long way from his previous life working in finance for UBS. It's a sacrificial ministry – you won't get rich as a youth mentor..

Greg doesn't look to convert people. Instead his faith is there in front of people and his actions speak more than words could. It's an evangelism that works through works and actions and example. In many ways it's a very modern ministry, but this kind of model stretches way back to St Francis of Assisi and his bold incarnational ministry.

I ask Greg if he's ever thought of becoming a church pastor. After all you can't be a youth worker for ever, can you?

'No, I wouldn't want that. The millennials are missing from church. A job like this means I can be near young people and be part of my neighbourhood.'

His work, and that of Young Life International, is all the more impressive when you realise that Greg's ministry is done in a public school, and not a faith-based one. He has to tread carefully. But everywhere we go people stop to say hello to him and to chat. He is part of this community and part of this school.

As we prepare to leave we pop into the school office to say goodbye. Jane is one of those omnicompetent people who work in the school office and keep the whole thing moving. They are at the heart of any school and every school has one.

'Greg is amazing. I don't know what I'd do without Greg.'

As we leave she calls to us.

'Thank God for Jesus.' Indeed.

Rev Steve Morris is the parish priest of St Cuthbert's North Wembley. Before being a priest he was a writer and ran a brand agency. In the 1980s he tried to become a pop star. Follow him on Twitter @SteveMorris214