"YOU describe my book as a 'secular warning against idolatry', and I accept that. And that may suggest that the differences between secular and religious views may be more fluid than we sometimes think."

The public debate on What Money Can't Buy by Michael Sandel (Allen Lane, 2012), arranged by St Paul's Institute, with JustShare, the LSE, and Penguin Books, was mem­orable for several reasons: an audience of nearly 2000, including many students and many who said they had not been in St Paul's Cathedral before; an attentive atmos­phere; some well-aimed questions; and, above all, Professor Sandel's brilliance as a teacher, and his insist­ence that philo­sophy be public - that philosophy helps us to think about the great issues of the day (News, 1 June; Features, 15 June; Books, 22 June).

But, as far as I was concerned, the key moment was Professor Sandel's affirmative and at the same time questioning response to my sugges­tion that his book was a "secular warn­ing against idolatry".

By "idolatry", I meant the way in which money had moved from being an instrument of exchange into a dominant force in nearly every aspect of life, demanding sub­mission and arousing emotions of both irresistible attraction and fear.

Having accepted the description, Professor Sandel went on to suggest that if it was right, we should re- ex­amine some of our assumptions about how secular and religious view­points differ.

THIS seemed like an invitation - deeply relevant to our thinking about money, but about many other things, too. "The secular": this age - with its disciplines of science, the humanities, social sciences, and economics, among others - seeks to understand the world (as the Latin tag quoted by Dietrich Bonhoeffer has it) etsi Deus non daretur - as though God were not a given.

Understanding the world in that way, Bonhoeffer asserted, was something that faith in God required of us. Understanding the world as though God were not a given can teach you a great deal about the world - we all know that. But Professor Sandel's response suggests that understanding the world in that way, through the eyes of disciplines that do not start with God as a given, may also teach you more than you expect about God and faith in God.

More than that, his response also suggests that disciplines that do start with God as a given - for instance, Christian theology - might be able to teach things about the secular world that it cannot teach itself. Such are the fertile possibilities that emerge when we recognise that "the differences between secular and religious views may be more fluid than we sometimes think."

The hour-and-a-half spent with Professor Sandel may therefore be an invitation to contemplate our world, and especially its current financial turbulence, in a way that exploits the possibilities of a genuine two-way traffic of thought. It is not just a matter of finding out "what the Christian gospel has to say" to the world of finance and the uncontrolled marketisation of our lives, but what we learn about God and God's purpose for the world by examining those aspects of our life through the secular dis­ciplines of our time.

Professor Sandel's comment should then be taken up not just with the relief that comes with sens­ing op­portunities for re-establishing Chris­tianity as having relevance to the public issues of our time, but with the excitement of exploring faith it­self, and redis­covering it for ourselves within the public square, with its triumphs and disasters, its knowledge and un­certainties.

It is not a coincidence that such an invitation to a more mutual journey of discovery occurred within a discussion about the place of money in our world; for money is no bad place to start on that exploration. The crisis around money - debt, the euro, the world's banking systems - is at the top of politicians' and financiers' agendas. They deploy every ounce of skill they can muster, and draw in every expert they can find.

In the process, they rediscover forgotten wisdom, and ancient vir­tues such as prudence and restraint, as well as ingenuity and vision. They even discover, if not, solutions then at least ways forward. To put it at its most hopeful, they refresh the mem­ory of those of us who call ourselves people of faith that it is the universe, and not just believers, that a loving Creator made, who longed for its good and surrounded it with guid­ance and commandments that were for its lasting advantage.

So ethics is increasingly a concern not just of the religious, but of many people seeking a more durable frame­work for our economic life. The Churches have not (and this should be a matter of regret) en­gaged with the demanding disciplines of economics and social science in a way that would have made a long-standing Christian ethical tradition more accessible to those at the sharp end of decision-making: no wonder that so many of the finance-sector profes­sionals surveyed by St Paul's Institute said that they did not think the City needed to attend to the guidance of the Church (Comment, 4 November).

YET the invitation to us is not that we should place our trust in the secular on its own terms. Looking at money and what has happened to it as an example of potential and actual idolatry brings to the table other insights than those that unaided secular disciplines can provide.

By speaking of idolatry, we lay bare the fact that money has become a rival to true faith, a serious com­petitor against God for people's loyalty. So we bring to bear the whole theological tradition of prophecy against idols - of martyrs who died rather than misdirect their wor­ship, and, above all, an account of the serious consequences of allowing that which is made by human beings to command their total sub­servience.

A secular warning against idolatry takes us a long way, but it also displays what we need, beyond secular thought, to counter the pervasive tendency of human beings to idolise what they have made, and to fall victim to good instruments that run out of control.

That is why the Doctrine Commis­sion devoted a chapter of its report Being Human (CHP, 2003) to money as a profound influence on human life. It is why the St Paul's Institute is determined to continue its engagement with the City; and it is why Christian people should see the fluid boundary between sacred and secular views as an exciting invitation to an arena where God is to be found.

The Rt Revd Dr Peter Selby is a former Bishop of Worcester. He is a member of the Interim Directing Team of St Paul's Institute