THE first thing you need to know about Poor Clare, Chiara Atik’s award-winning play about the lives of St Clare and St Francis, is that it’s funny: really, really funny.

The saints lived in the 13th century, as Eleanor Bull’s simple set and gorgeously ornate period costumes make clear. But the bantering, anachronistic language is that of a Hollywood teen romcom: “Cool! Good for you guys!” When this is set against choral chants and monastic ritual, the incongruity is irresistible, and the laughter never stops.

The second thing that you need to know is that the play is absolutely respectful of the faith of Clare and Francis, and the convictions that drove them to renounce the privilege into which they had been born in order to live with and for the poor. The arc of the piece is historically accurate, and we become deeply involved with the reluctance, the false starts, the compassion, and the sheer grit that took Clare away from wealth into a convent.

Those who will be hardest hit by this terrific drama are Christians who faithfully donate to foodbanks while living in detached houses, knowing deep down that this doesn’t even begin to address the world’s need. “I’m still going to do charity,” Clare says early in the play, trying to reconcile Francis’s sacrificial teaching with the lifestyle into which she was born. “There is a middle ground.” But there isn’t. There really isn’t.

Arsema Thomas, a familiar face on Netflix, but making her stage debut, is absolutely assured as Clare. A charismatic kindness flickers under the surface even in the opening scenes, when all that she can think about is the hair that her servants (Liz Kettle and Jacoba Williams, nicely individualised) are intricately arranging. Her scenes with her self-absorbed sister Beatrice (a delightful comic turn by Anushka Chakravarti) are both barbed and tender, as the younger girl struggles with her bewilderment at the change in Clare.

Freddy Carter portrays a charming Francis — pragmatic, teased, and never saintly — becoming more nuanced about the realities of the world as Clare becomes more radical. This is all staged with a bustling energy by Blanche McIntyre, subtly reminding us of the relevance of the incisive writing by introducing for brief moments a beggar in a hoodie, a rough-sleeper’s tent of plastic sheeting, and a homeless man asking for spare change on a commuter train.

The final scene shows Clare at prayer in a 21st-century nun’s habit, and she names areas of desperation locally and globally. It is perhaps over-emphatic, since anyone in the audience with a shred of empathy has made these connections for themselves. But the final plea to God to help us to know what to do in the face of such overwhelming need is absolutely recognisable. Challenging it may be, but, saints preserve us, it is a soul-restoring joy from beginning to end.

Poor Clare continues at the Orange Tree Theatre, 1 Clarence Street, Richmond, Surrey, until 9 August. Box office: phone 020 8940 3633. www.orangetreetheatre.co.uk