The last time St Paul's Cathedral was so much in the news was the wedding of Charles and Diana: a vast if moth-eaten musical parade which ended very badly when the fairytale wedding turned into a marriage of unfaithful human beings. That helped turn the cathedral into a major tourist attraction, though it did nothing for the Christian message. Now another piece of theatre has swept it up, and with it won a turn on the national stage.

Protesters hoping to "Occupy the London Stock Exchange" were prevented from entering Paternoster Square, a shopping development which had been their original target, and instead have camped, in orderly rows, around the north side of the cathedral and across its main west entrance. This rather messy and absurd situation has handed the dean and chapter of St Paul's a truly historic opportunity to discredit Christianity in this country. They seem determined to take it. They should think, and stop.

The dean and chapter appear to have decided that health and safety considerations mean they must be rid of the makeshift camp. These grounds are frankly risible. Pretending otherwise compounds the first mistake, which was to shut the cathedral altogether, rather than expose visitors to the sight and smells of a couple of hundred protesters. A cathedral isn't really there for the tourists, even if it can charge visitors £14.50, as St Paul's does. It is a place for prayer and worship. The congregations who come for these, the real purposes of the building, should remember that Jesus talked to publicans and tax collectors. He might even have talked to merchant bankers. He would certainly have talked to the protesters camped outside.

Aspects of the protest camp are silly and rather squalid. But it still represents a profound and important moral revulsion which the Church of England needs to take seriously. These aren't the usual Spartist suspects. The sense that there is something outrageous, unjust and absurd about the world of modern finance has spread across the whole political and religious spectrum. Even Pope Benedict XVI has reinforced his predecessor's teaching with a demand that the markets of the world be brought under human control. The Church of England needs to be part of this discussion, for its own sake and for the sake of the country. And that is done far more effectively by theatre and by conversation than by lecturing or even preaching. It is no use having clever bishops saying clever things that no one listens to. Here at St Paul's right now, there is a chance to catch the attention of millions of people who would never listen to a bishop or recognise a Dean without a Torvill.

The protesters aren't right about everything. A lot of the time they aren't even coherent enough to be wrong. But the role of the church is to talk with them and to find out how their sense of injustice at the present slump can be refined and educated and brought out into the wider conversation. The cathedral has a chance to take Marx's taunt about religion being "the heart of a heartless world" and try to make it true, and valuable. It must not fumble this.

If the dean and chapter continue their steps towards evicting they will be playing the villains in a national pantomime. There will be legal battles and, eventually, physical force. At every step, the cathedral authorities will be acting in the service of absurdity and injustice. Yet this is where the logic of their position is leading them. They must see this, and stop. Jesus denounced his Pharisaic enemies as whited sepulchres, or shining tombs; and that is what the steam-cleaned marble frontage of St Paul's will become if the protesters are evicted to make room for empty pomp: a whited sepulchre, where morality and truth count for nothing against the convenience of the heritage industry.