Here in Hannover the talk is all about change. The conference Kirchehochzwei not only has nearly 1200 people attending today and tomorrow, but also is a feat of imaginative organisation. I seem to do a lot of stuff in Germany, but this one has been hugely challenging, stimulating and educative.

The great thing about being out of one's own culture is that you get to look through the lens of another – and then look differently at your own. Perspective changes and new insights are gained – a bit like changing the camera angle or lighting on a film or stage set.

The conference is aimed at opening up German Christians' thinking about how to address necessary change in how the church shapes itself in a changing world. Learning from some of the Fresh Expressions experiences in England, they now want to work out what this might look like in a German context that is simultaneously both similar and very different. Yesterday I saw three superb presentations about initiatives in Austria, Aachen and Erfurt: two of these were Roman Catholic. And that into to the really interesting thing about the nature of the conference itself: it is put on by both the Evangelical (Protestant) and Roman Catholic Churches in Niedersachsen, sponsored by both the bishops.

What is interesting about this is that the ecumenical nature of the event both raises and lowers the guard as critical questions are asked from every possible direction in the exploration of how the 'church' is to change and what changes are legitimate. In my various inputs I have been stressing the importance of 'order' in new forms of church – a bit like the clarity and creativity made possible by painting white lines on a tennis court, without which no game is possible, no creative play is feasible and all you can do is bang a ball around.

Plenary sessions this morning gave way this afternoon to workshops and seminars – hundreds of them. It is amazing to watch it happen. I had been asked to attend a theological workshop on so-called 'liquid church' at which Thomas Söding, a Roman Catholic academic New Testament scholar, presented a brilliant paper in which he took three images from the New Testament of crises in boats. The opening paragraph of his notes (my quick translation) says:

The New Testament is not a model kit for the ship that is the church; rather, it is a log book that establishes the story of its early journeys, a fuel station which fills and empowers it, and a GPS satnav by which it can navigate.

The concluding observations in his notes state:

[This conference] is St Peter's little ship on a great journey. Without a general overhaul and a new crew it will go down like the Titanic. But which renovations are needed and which crew selection is the right one, if the ship is not to sail under the wrong flag and is safely to reach its destination with its freight intact, is the master question.

Not a bad question to pose at the end of the week in which Pope Benedict announced his retirement. And the has been a lot of questioning here about what might happen next in the Roman Catholic Church under a new Pope.

Following questions and discussion from the audience, I was asked to make a few observations on the question of how to change the church in ways that are creative, yet consistent with the New Testament. In reply I noted how one contributor yesterday had said of his 'fresh expression of church' in Aachen, “For me it is an experiment,” and added that in my view “the church itself is an experiment”. Picking up on Tom Wright's notion of biblical history as a five-act play in which we are still writing he fifth act, I suggested that however creatively and innovatively we develop the plot, it must always be consistent with what has gone on in the first four acts. Furthermore (and clearly mixing my metaphors here), although we might find ourselves responsible for steering a new and uncharted course in today's sea, we must not lose sight of what it actually means to be a 'ship' in the first place.

There was loads more. It was interesting later to listen to a moderated conversation between the Protestant Bishop Ralf Meister and his Roman Catholic counterpart Norbert Trelle. They didn't duck any questions either – including the 'challenge' to both churches of how to 'celebrate' in Wittenberg in 2017, the 500th anniversary of the start of the Reformation.

In all this we have witnessed people changing the guards that protect them from discomfort or challenge. It is a very good thing.

Anyway, that's enough. I am giving the final address in the final plenary session tomorrow afternoon. I have been asked to inspire and encourage the thousand people there. No pressure there, then.

Then I go for dinner with friends before preaching (this time in English, fortunately) at an international service in Hannover on Sunday before catching a flight back to Bradford via Amsterdam.