You know about the Transition Movement. Its central aim is to help communities restructure the way they live in a way that uses very little oil, partly because our oil use is warming the planet too much, and partly because the oil is anyway running out. The whole pattern of modern life is centred around cheap and available oil, and we have become comfortably dependent on it. But we have passed 'peak oil' and we need to start thinking creatively about how we are going to live after it is gone. So the buzz words are resilience and sustainability.

Now I know we have eco congregations, although they are still largely about lightbulbs and churchyard gardens. You might fondly think that using a bit less electricity is doing your bit for turning the tide of global warming. It isn't – not even close. And it's great if Christians can get involved in the Transition agenda, not least because it calls for significant personal change in local communities, and the Christian faith has a lot of wisdom and power to bring to that.

But don't our churches themselves need a Transition agenda? Just as oil is running out, isn't Christendom running out too? Our churches have long been dependent on the power of Christendom, making all kinds of things possible that local Christian communities could not have done on their own. Christendom made church a very comfortable place to be. As Christendom runs out, many of the ways we are used to 'being church' are becoming unsustainable. We can improve our welcoming processes, we can take out the pews, we can use PowerPoint in the sermons, but these are lightbulb measures. We need to help our churches become resilient and sustainable Christian communities, not dependent on the structures and support of Christendom for their future.

The danger with the 'mixed economy' is that our existing church communities are being assured that they will continue to have a parallel existence much as they are. But if Christendom runs out, most of them won't; and they will run into the coming era ill-equipped to be resilient and sustainable church. In the present battle over resources within the mixed economy, fresh expressions are already beginning to feel the heat. Here in the Diocese of Exeter, out of the 40 or so 'mission posts' promised in our restructuring five years ago, only a handful have seen the light of day and now there is a moratorium on them because of lack of resources. The future of the church could fall between two stools.

David Muir is an Ordained Pioneer Minister in the Okehampton Deanery of Exeter Diocese. With a long background in adult Christian education, he is now supporting 24 largely rural parishes to create fresh expressions of church that will resonate with the increasingly diverse population of Devon. He is also course leader of The Pioneer Disciple, an Anglican/Methodist Devon adaptation of the mission shaped ministry course (see www.exeter.anglican.org/pioneer), and he writes a regular column on how to do church in a 'pioneer' way (see www.exeter.anglican.org/pioneerprimer).

If you have something burning to say and want to contribute to the Share weekly guest blog, please contact Karen Carter. The views expressed in this blog are those of the author and are not necessarily shared by the Church of England, the Methodist Church, the United Reformed Church, Church Army, Fresh Expressions or any of its partners.