It's probably a desire to make our subject seem interesting that inspires this conspiracy of silence - plus the conviction, fostered by generations of teachers, that those who find things boring are boring themselves.

Nevertheless, there is no escaping the fact that John Osborne's Luther (1961) is a three-and-a-quarter-hour bum-number. It's impressive but boring, intelligently staged but boring, well-acted but boring. Imagine an interminable history lesson relieved only by occasional trips to the school chapel to listen to God-bothering pi-jaws from the pulpit, and you will get some idea of just how punishingly dull this play is.

Like so much that is tedious in the theatre, the play was heavily influenced by Bertolt Brecht. It consists of a series of illustrative scenes depicting Luther's life, from his earliest days in an Augustinian monastery to his excommunication and the peasant wars that followed. There are big set-pieces, like the Diet of Worms, when Luther refused to retract his condemnations of the Catholic Church, and more intimate moments, when he provides us with far more news than we need to know about his chronic constipation. Even his great moment of spiritual revelation is accompanied by a blissful evacuation. I put it down to that ghastly diet of worms.

This epic revival in the Olivier is well-timed. After the terrible events of September 11, we are evidently entering a new period of religious wars. And the legacy of Luther, and the Reformation, live on in the continuing anguish of Northern Ireland. Osborne had a mighty, enduring theme here - the horrors committed by man in God's name - but, throughout, one senses authorial perspiration, rather than inspiration.

There are flashes of echt Osborne. The spiel of the indulgence seller, Johann Tetzel, played with unforgettably greasy insinuation by Richard Griffiths, comes across as one of Osborne's beloved music-hall shticks, while Luther's sermons blaze with the intemperate fire of a God-inspired Jimmy Porter.

But these scenes also serve as reminders that Osborne was far better at full-throttle theatrical monologues than at dialogue between subtly observed characters, and much of Luther comes over as a trudge of a pageant play.

The director, Peter Gill, stages it with great assurance and clarity, with the help of a fine, imposing design of ecclesiastical arches by Alison Chitty, but there is no mistaking the fact that much of the writing has all the dynamism of a school textbook.

As if to compensate, Gill parades a large chorus of chanting Augustinians as if they were the monastic equivalent of the Rockettes. They glide round the stage with a precision the producers of Holiday on Ice would envy, and bow their heads in prayer with spooky synchronicity - not so much the Roman Catholic Church as Roman Catholic Kitsch.

Rufus Sewell is a suitably anguished Luther, all charismatic cheekbones and painful belly gripes, and he memorably charts the way in which the character's spiritual despair is transformed into dangerous conviction. There is strong support, too. Malcolm Sinclair is hypnotically subtle and devious as Cajetan, the Cardinal who tries to persuade Luther to recant, with a mixture of smarm and menace; Geoffrey Hutchings provides some welcome humour as Luther's irreverent dad, complaining that a wine glass is as empty as a nun's womb; and Timothy West gives a lovely performance of spiritual humility and wisdom as Luther's confidant, Johann von Staupitz.

Despite all their endeavours, however, Luther remains a long, hard slog.

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