Last night I woke up in the middle of the night and couldn't get back to sleep. We've all been there – things started ticking over in my mind. The stuff I had to do today, the things I didn't get done yesterday, and, as the increasingly popular meme has it – stuff that happened a number of years ago...

Usually when this happens, I try to persevere and force myself to sleep. This is against all the advice as to what you're supposed to do. Reading for a while or getting up briefly to effectively re-set the sleeping process is apparently what's best. Instead, I usually lie there and my lack of drowsiness encourages frustration which encourages further sleeplessness in a spiralling feedback loop that leaves me looking like Eddie Izzard the day after he ran 27 marathons in 27 days.

Except this time I didn't do that... I prayed. Not in a sort of free-form, conversational way, but in a very repetitive and structured way. I used the Jesus prayer. And it worked. I drifted off to sleep quickly and peacefully and awoke feeling ready to face today's torrential rain and the District Line...

But it got me thinking; this ancient prayer isn't simply a sacred version of counting sheep. It's been a refrain of Christians around the world for generations. But I've been surprised how many Christians today – especially younger evangelicals – aren't aware of the Jesus Prayer. I remember one conversation with a friend who's a life-long believer, but had never heard of it. This left me wondering how many others are missing out on this God-given resource.

What is the Jesus Prayer?

There are various forms, but they all centre on the following form of words:

"Lord Jesus Christ, Son of God, have mercy on me, a sinner."

It's more than just those few words. It's the cornerstone of a whole realm of Orthodox spirituality. One writer describes the Jesus Prayer as, "More than just a prayer; when done in accordance with the teachings of the Church Fathers it becomes a way of life, and a vehicle for the Holy Spirit. It is a little phrase that becomes a catalyst to change the one who undertakes it to the very core, this is why it is so powerful. It has the ability to change a human being into a servant of God."

Where did it come from?

The prayer is based on ways that Jesus taught His disciples to pray. So, in John 16:24, He told them, "Until now you have not asked for anything in my name. Ask and you will receive, and your joy will be complete." The main essence of the prayer, asking for God's mercy, is related to one of the earliest prayers of the Church – the Kyrie Eleison, which literally means Lord have mercy. This prayer of penitence is included at the beginning of Eucharistic liturgies – in other words, before coming into the presence of God, those praying must acknowledge their need for mercy, and request it from God.

Who uses it?

The Jesus prayer began in Eastern Christianity. It is thought that the Desert Fathers and Mothers developed the use of it. These Christians who retreated to the desert before and during the Christianisation of the Roman Empire gave us so much of our understanding of what prayer and worship might look like. So, the Oriental and Eastern Orthodox Churches (together comprising almost 400 million Christians worldwide) have used the Jesus Prayer since their early days. But its use isn't limited to Orthodox believers – Roman Catholics (and especially Eastern Catholics) use the prayer in their private devotions. The writer and Franciscan Friar Fr Richard Rohr has said, "Relying upon mercy, in fact, protects you from the arrogance and pride that wants to judge others, even in your mind. It situates you in freedom from any sense of your own sufficiency or superiority, and affirms a non-need to justify yourself, and thus keeps your heart open for others and for God."

Protestants of many kinds have also found the Jesus Prayer to be profound. Shane Claiborne included various references to it in his Common Prayer project, while evangelical Anglican theologian NT Wright writes, "The "Jesus prayer" has been rightly popular... This, like the Jewish Shema, is designed to be said over and over again, until it becomes part of the act of breathing, embedding a sense of the love of Jesus deep within the personality."

Why the repetition?

Some Protestants might be wary of the tendency to 'vain repetition' which is inherent in the Jesus Prayer. Such repetition was something the Reformers railed against. But to simply brand all users of the Jesus Prayer as such would be to fundamentally misunderstand the context in which it was developed and in which it is still used. The technical word is 'Hesychasm' which is used to refer to the Orthodox tradition of praying inwardly, and attempting to find union with God beyond language. In this sense the Jesus Prayer is something of mantra – but the key difference between the Jesus prayer and other mantras of eastern religions is in the title – the aim is to bring a Christian closer to Jesus.

How should I pray it?

You may be lying in bed struggling to sleep as I was. You may be in a church, a park, or even in the wide open countryside. The prayer is one in which an individual comes close to God – in that sense it's very different from the Lord's Prayer or the Grace which are meant to be said corporately.

Praying the Jesus Prayer isn't a fast-track to some kind of spiritual enlightenment. It's tough at times – in fact there have been occasions when all the external conditions were 'correct' – I was sitting in a quiet chapel in an attitude of prayer for example, but I still found myself distracted and not able to pray for longer than a few seconds at a time. But it can and does work.

The key thing is to try it. As Jesus says in Matthew 6:6, "But when you pray, go into your room, close the door and pray to your Father, who is unseen."