CHRISTIANITY, no less than other religions based on ancient scriptures, has a problem when it comes to ethics. How can centuries-old writings help to resolve new moral problems such as GM crops, WMDs, or developments in medical science of which the ancient writers had no inkling? To most outside religious communities, the answer seems simple: they can’t. But committed believers, too, find it difficult to say what they are doing when they bring the Bible to bear on contemporary moral problems. Even if we want the Bible to be an instruction book (and not all of us do) working out what the Bible teaches about genetic manipulation or using stem cells for therapeutic purposes is far from simple.

In a book published this week a Cambridge vicar offers a fresh way to characterise what Christians are doing when they try to make sense of their moral life. Samuel Wells’s Improvisation: the Drama of Christian ethics (SPCK), draws parallels between what is happening when actors improvise a drama, and what is happening when Christians act out their faith. Dramatic improvisation is not, Sam Wells says, nearly as simple as it looks. Even if improvising actors are literally making it up as they go along, it has taken hard work in traditions of acting and hours of rehearsal to reach a point where they can act in ways appropriate to the dramatic circumstances. Practice forms actors in the habits that make improvisation possible and helps to build the mutual trust without which improvisation cannot work.

When Christians pray, worship, read the Bible or share the sacraments they are, suggests Sam Wells, forming character habits that help them to discern the will of God when fresh circumstances, such as difficult moral issues, present themselves. This isn’t the same as always being original. If improvisation always required originality it would feel as dreadful as the pressure always to be funny at parties. Christians, too, are not trying to be original but to act in the space between God ’s act of creation and God’s promise of redemption with habits of character formed by their years of life together.

A skill that Christians learn, like improvising actors, is when to block a suggestion made by another actor and when to accept it by incorporating it into the evolving story. A nervous improviser is likely to block suggested lines that seem to lead her away from the previously agreed plot outline. A more accomplished improviser can accept a new lead and transform its risk into an opportunity to enrich the drama without losing the story’s thread. Christians, Sam Wells suggests, are tempted to conceive their lives in terms of givens from which they dare not deviate, instead of gifts that they can accept and transform into opportunities within the drama of God’s story of love for the world.

Imagining the Christian life as an improvisation acted by characters shaped by Bible reading, worship and sacrament is exhilarating, but is it true? Sam Wells is sensitive to the accusation that “improvisation” is too trivial and ephemeral an activity adequately to describe the serious business of Christian life, and encourages Christians to resist being more solemn than God. But I share with Milan Kundera’s narrator a need for some heaviness to save me from “the unbearable lightness of being”. Kundera’s narrator wonders if heaviness is truly deplorable and lightness splendid? He is horrified that “we live everything as it comes, without warning, like an actor going on cold” because “what can life be worth if the first rehearsal for life is life itself?” Wells is right that Christians have to work hard at their spontaneity. Kundera is right that unremitting lightness is unbearable. It is only some combination of these two insights that will keep us from the bleak, pointless mumblings of characters who act in Becket or Pinter plays, and draw us instead into the drama of God.

Stephen Plant, a Methodist minister, teaches theology and ethics in Cambridge