Marty Sampson, the Hillsong worship leader, is only the latest prominent Christian to be on the brink of leaving his church, having said he is "losing" his faith but not renounced it completely - yet. He has cited various factors, as others do, too. But there's one issue that stands out.

It's not that they cease to be seekers after truth. Nor that they necessarily cease to be Christian. Rather, it's that the church ceases to be the place they believe they can find this truth. They lose confidence in faith-based organisations.

The trend has been researched in the UK by Steve Aisthorpe. His book, The Invisible Church: Learning from the Experiences of Churchless Christians, reports the results of asking the many people who stop attending why they left. The conclusions are unexpected. Amongst the reasons for departure, the desire to explore faith in another setting is key.

Churches become off-putting in various ways. They become poisonous because of clashes between personalities. Their spiritual life is marginalized because of a desire to provide public services. Their leaders become preoccupied with the inward-looking, anxious concerns of the denomination to which they belong.

In short, church agendas become more important than the Christian life for which the leavers yearn. Life in all its fullness must be sought elsewhere.

Other research on the origins of religions suggests why this dynamic dogs churches, as well as the institutions of other religions. The evolutionary psychologist, Robin Dunbar, is the leader of a team of scientists and theologians pursuing a new account of how religions arose in human evolution.

He argues that it stems from the discovery by our paleolithic ancestors that they could induce trance experiences. These immersive altered states of consciousness gave them access to spirit worlds. The cosmos became a multi-dimensional place. Shamanistic rituals and animistic gatherings became commonplace, as is evidenced by cave art and burial practices.

Then, over time, the experience of ecstasy became formalized in what Dunbar calls "doctrinal religions". Hierarchies of priests and impressive temples emerged, as did systems of belief and texts like the Bible and creeds.

However, this created a tension that runs through religions to this day. On the one hand, doctrinal religiosity helps keep the faith going and means it can spread far and wide. But on the other hand, the ecstatic wellspring of the faith can become eclipsed.

The upshot is that the history of religions are full of revivals and awakenings that attempt to revive dying doctrines and ossifying organisations, if not overthrow them altogether.

In other words, when people leave churches today, they are replicating what our forebears have been doing for generations. They want to renew their contact with the source. They leave church to find God.

Of course, defenders of the church will argue that people need community to find faith and that the Bible argues that church-going is integral to being a Christian. However, I think this is a misreading of Biblical translations. The word for "church" is usually the Greek, ekklesia, which means "assembly" or "gathering". Confusing that with an institution is actually part of the problem.

Early Christians got together because together they found the life of the spirit. Steve Aisthorpe believes this is happening in new ways now, hence the title of his book, The Invisible Church. And not surprisingly, we are seeing new forms of ekklesia sprouting away from the institutional church, online and informally.

If people cannot connect with God in the institutional church setting, we can expect to see more prominent Christians leaving their positions of leadership.

Church institutions feel under threat in the modern world. They are used to having status in western societies. They feel they must play a part in the local, secular community.  The risk is that they forget their primary goal: to foster the personal transformation that opens what Jesus called the eyes that see and the ears that hear.

In other words, they are so focused on the kingdoms of this world that they forget the heavenly kingdom.

Mark Vernon's new book, published this month, is A Secret History of Christianity: Jesus, the Last Inkling and the Evolution of Consciousness. For more information see www.markvernon.com