THE choice of a deconsecrated church as the venue for Sir Kenneth Branagh's return to the Shakespearean stage, in the role of Macbeth, set up interesting resonances. The language in a play that deals with "the ungodly, the unholy, and the irreligious" would sound different in a church, the actor suggested beforehand, and would add to the sense of desecration on which the story depends.

He had a point. But it was not the defining metaphor for the performance in the former Anglican church of St Peter's, in Ancoats, as part of the Manchester International Festival. The building's stained glass still carries Petrine keys, and the set designer, Christopher Oram, had hung a gigantic Celtic cross before them. Yet he had also transformed the nave into two facing jousting stands and filled the space between them with soil upon which heavy rain poured during a dramatic opening battle.

Within minutes, the stage was turned into a quagmire of inches-deep mud. As the play progressed, this mud became the key metaphor for the moral pollution that infects the central characters. It clung to the feet of all, and defiled the trailing fine woollen gowns of Lady Macbeth and the other female courtiers. The actors affected not to notice it; but the audience could not forget it.

There are many ways of considering evil. The dominant mode these days is psychological, as was clear from the recent demand by the murderer Ian Brady that he should be treated as bad, not mad. Mr Brady's attempt to be transferred from a mental hospital to a prison was an attempt to score points over others whom he regarded as less intelligent than himself.

There are dimensions to Shakespeare that sit happily with that view. Iago's animus against Othello, like Shylock's against the Venetian merchant Antonio, are easily thus portrayed. So is the monstrous nihilism of Richard III in a play that was, for Shakespeare, in many ways a prototype for Macbeth.

But Macbeth's is a different kind of evil, and one that is not so susceptible to post-Freudian interpretation. Branagh's Macbeth begins as a decent enough chap before he is lured by the witches' words into fulfilling what they prophesy. He is not a man without religion so much as one in thrall to a malevolent version of it. He knows right from wrong, and is torn, his mind full of scorpions, as he flickers in and out of madness.

This is evil as possession - a notion of which the monarch of the day, James I, approved - so that Macbeth never feels any pleasure in the fruits of his Machiavellian ambition, and what he desires slips ever further from his grasp. He ends as a man with nothing left to lose.

But this is a world in which evil is a metaphysical reality rather than a psychological metaphor. The dagger floats in the air, not just in his imaginings. The banqueting table physically divides to allow Banquo's ghost through. The audience feels the intense heat of the flames of hell, just as they are showered with sparks from the clashing swords of the battles. And the walls of the theatre, like the clothes of the audience, are spattered with mud as Macbeth is spattered with blood at the close. This Macbeth takes us back from the psyche to the soul.

Pope Francis: Untying the knots by Paul Vallely is published by Bloomsbury on 1 August.