Sarah Crompton: In times of political turmoil we need great art

I had one of those conversations with my bank the other day, in which I had managed to lock myself out of my account and couldn't remember any answers to any security questions. "Well, who's your favourite author," the very patient man at the other end of the phone enquired. I had four incorrect attempts before he gave up.

But if he'd asked me to name my favourite modern play, I'm pretty sure I'd have said Brian Friel's Faith Healer. I first saw it in a revival of the Abbey Theatre's production at the Royal Court in 1992, a version so potent that I can look back on it now in vivid, overwhelming detail, recalling not just the broad brush of Donal McCann's performance as the fantastic Francis Hardy, faith healer, but single moments of it: the way he raised his head as he accepted his fate, the confusion in his bright eyes, the rasp of his voice.

A sign of Faith Healer's greatness is that it is capable of sustaining radical reinterpretation

Sinead Cusack was his wife Grace, and Ron Cook was Teddy, the loyal manager. Very young he must have been, because almost 24 years later he returns to the part in Lyndsey Turner's magnificent, mesmeric production at the Donmar Warehouse, with Gina McKee as Grace and Stephen Dillane as Frank. Cook is wonderful, wringing every ounce of meaning and feeling out of every line.

But Dillane and McKee are magical too, creating entire people in front of your eyes, barely moving, but revealing everything about their wounded hearts. It is a sign of Faith Healer's greatness as a play that it is capable of sustaining radical reinterpretation; you want to see what different actors make of it. Dillane makes Frank's delivery much lighter, more amused than I ever remember before; his eyes seem to be seeing something that is hidden from you.

The play revels in the gray areas, the uncertainties, the mysteries of life

What also makes Faith Healer such a significant work is its deceptive simplicity. Friel sets three stories in front of you, in order to build a picture of one event. But each remembrance is different. You have to listen carefully, not just to the repeated phrases that form a kind of incantation running through the play, but to the details that change, the events that take on new shapes. It is you, sitting there in the dark, who becomes the ultimate receptacle of confidences; these people have no one to talk to but you. Your interpretation of what you hear and see is your version of their truth.

It is astonishingly intricate once you start to think of it. And that ultimately is what for me makes Faith Healer such a towering achievement. Like all Friel's work, it is a play about doubt, a work that mines the cracks between things, that revels in the gray areas, the uncertainties, the mysteries of life. Watching it the other night, in a country now divided more strongly than it has ever been, where people shout with loud conviction, its quiet belief in the complexity of things was like a balm to the soul. It felt almost healing.