When did your church last Skype the Vatican? Or when did you see Tim Hughes get a congregation from over forty nations, aged seven to seventy, dancing to 'The Way' in a Cathedral? (After singing rounds of contemplative Taizé chants...)

This formed the climax of 24-7's global gathering in Vienna, to celebrate 15 years of flourishing. 24-7 Prayer is "an international, interdenominational movement of prayer, mission and justice working in more than half the nations on earth." Cardinal Schönborn, the Roman Catholic leader in Austria, had personally invited 24-7 to hold a gathering in his palace and the neighbouring Cathedral while he was discussing other matters in Rome.

I was a 24-7 novice, but something about the simplicity and diversity of this global prayer gathering caught my imagination, and I thought that travelling from my new home in Pakistan to Vienna would be a fun adventure. It turned out to be a remarkable experience of unity that I had never encountered before. I was struck again by Jesus' supposedly unanswered prayer in John 17:21. It goes like this:

"I pray also for those who will believe in me through their message, that all of them may be one, Father, just as you are in me and I am in you. May they also be in us so that the world may believe that you have sent me."

I first noticed this prayer at university and got pretty excited. Sadly, my conversations with a range of Christian friends didn't suggest there was a great commitment to fulfilling this prayer, or a vision of how to do so. Discussion was always focussed on how to decide whether enough core doctrines were agreed on, with joint gatherings having an air of awkwardness at best, patronising suspicion at worst. So how were we ever going to reach the oneness of the Trinity? How would the world ever believe that Jesus truly subverts our patterns of judgement and separation if there was no unity?

In contrast, there was a freshness and humility in Vienna that gave us all new hope. Pete Greig, the founder of 24-7, writes in his international best-seller, Red Moon Rising (revised in April) that prayer is a "bridge, a clearing in the forest, a meeting place for Christian unity" and a "shared language for the tribes of Israel." What gives the 24-7 movement particular weight to its unity is historical and geographical roots.

Greig, brought up in a charismatic tradition, recounts his discovery of the Moravian Church's commitment to unity and prayer. The Moravians' prayer movement began in 1727 as they repented of their previous critical and divisive attitude and experienced a spiritual awakening. Count Zinzendorf, the founder of the Moravians' 24-7 prayer movement, claimed the motto: "In essentials, unity; in non-essentials, liberty; and in all things, love."

Since then, Greig has seen the 24-7 movement spark in the Roman Catholic Church in Austria, through the charismatic Loretto community. The members of Loretto demonstrated abundant hospitality to us in Vienna, from clearing the tables to setting up the Cathedral for over 700 participants in addition to several intrigued Viennese visitors. For the Cathedral to welcome such a large sprawling band of people, with guitars, drums, and dancing was very generous.

The highlight for me was the Skype call to the Vatican. Cardinal Schonborn's beaming face with St Peter's Basilica in the background was transmitted onto the screens of St Stephen's Cathedral. Pete Greig beamed back and had a chat with him about everything from prayer to the Syrian refugee crisis. In case there was any doubt about the sincerity of this cross-tradition relationship, the Cardinal started by saying that Pope Francis wanted to send his personal greetings to the 24-7 gathering, and that he sought our prayers, which we duly offered. There was much more cheering and waving than I imagine the Cardinal normally experiences, but he seemed to enjoy it.

But does it all end in a nice service? By no means. 24-7 is also uniquely powerful in its unwavering commitment to go out from prayer – to change the world by demonstrating God's love in word and deed. We started the next epoch of 24-7 by offering clothes that had been brought from around the world for Syrian refugees who are coming in their thousands to Austria. Just as in Jesus' prayer in John 17, the love experienced in unity cannot but flow outwards to a world in need of God's grace.

I encourage you to try praying with some people who might pray differently from you. And then maybe try it 24-7 for a couple of days... In St Francis of Assisi's words, and the theme of the Vienna gathering:

"Now, let us begin."