Christianity in 21st century Britain is a peripheral affair. The church is a marginal voice and while it may still retain its status of significance in some matters, that voice carries little authority.

In the wake of the Manchester bombings it was the church that was invited to provide leadership at the vigil to commemorate the victims. Yet as the Bishop of Manchester has since said, it was his role to 'curate' the community's response rather than lead it, and certainly not to dictate it.

Five hundred years ago, at the moment in history we associate with the beginning of the Reformation, the church undergirded every facet of life. On October 31, 1517, a monk named Martin Luther legendarily nailed his 95 Theses on the door of the Castle Church, Wittenberg, and the church was never the same again.

Luther's radical rediscovery and application of the doctrine of grace blew apart the relationship between church and people, challenged the practices of the Catholic Church and paved the way for the Protestant movement to move from a persecuted minority to a legitimate expression of church. Five hundred years later, the dramatic shift in the positioning of religion and in particular Christianity, in the life of Britain and other western nations, has been so thorough and so fast that some have speculated if we are experiencing a second 'reformation'.

Where might we look for evidence of this transformation? There is first the story of decline, of all the mainstream denominations. Then there are stories of those who have left the church but not abandoned their faith, looking instead to gather a handful of like-minded individuals and journey together. Others are drawn to elements of Christianity, but are happy to fuse these beliefs and practices with those of other traditions and have little interest in organised religion.

Something is afoot. And whatever it is, Christianity, and its place in society, will probably never be the same again. The writer Phylis Tickle referred to what we are experiencing as another 'semi-millennial rummage sale of ideas', a kind of necessary clear-out of accumulated stuff as a means of rediscovering what really matters.

That was true of the Reformation with its three slogans, 'sola Scriptura' 'sola fides', 'sola gratia' – 'Only scripture!' 'Only faith!' 'Only grace!' It was attempting to clear away the clutter of indulgences, overbearing ritual, relics and obligatory religious observance, and invite people back to a personal and individual faith. The point of these slogans was to shift authority away from the patriarchal institutions of the church and back to scripture.

Some argue that the Reformation didn't go far enough. The power of institution was not sufficiently broken and ritualistic authority was simply exchanged for an authority of doctrine. After all, you couldn't trust the ordinary man or woman to interpret Scripture on their own!

So instead of being mediators of grace, the churches became arbiters of truth and dispensers of orthodoxy. What we are experiencing in our own age is the undermining of institution as the locus of authority. And with that global shift the churches in the West find they are losing adherents at an alarming rate. Some, it is argued, were never too firm in their belief in the first place. Some are taking their well-worn faith and looking for a place to nurture it beyond the reaches of organised Christianity.

Others still are venturing out to the margins and reimagining church for the increasingly post-Christian, embryonic post-Christendom landscape. Slowly but surely a movement of pioneers and dissidents is forming. Spirit and community are the axioms that characterise this reforming movement – the equivalent of the three-fold cry of 'grace'. There are signs that the church is finally emerging from the upheavals of the last century, and is at last growing in conviction and confidence, free from the assumptions and models of Christendom.

This new breed of believers views church as a set of relationships rather than a set of prescribed practices and is free to embrace treasures such as contemplation, silence and solitude, devalued by the Reformation, and refresh them for this new age. This new 'reformed' church is free from clericalism to find the space to rediscover church as a deep expression of solidarity and love in community. And it is freed from the endless dance around the holy grail of orthodoxy to journey with others to discover what it means to live Jesus' call to live life to the full.

These new forms of church are small and numerous, fleet of foot and flexible in form. They meet in cafes and community centres, pubs and gyms. They will never have the power, prestige or public face of the traditional church. This is 'a church from below', a church with a purpose shaped not by the limited arguments of the Reformation age of right belief, but by the common hunger for spiritual community and authenticity in the service of Christ.

Paul Bradbury is Pioneer Mission Coordinator for Church Mission Society.