At 15, Thérèse tried to rejoin Marie and Pauline in the Carmel, but was rejected as too immature — and possibly too damaged. However, she would not take no for an answer and persuaded her father to take her and another sister, Céline (also subsequently to join the Carmelites — the fourth sister Léonie also taking the veil but opting for another religious order) to Rome where she managed to snatch a few words with Pope Leo XIII to ask for his help. The nuns back in Lisieux yielded and she joined in 1888.

Her almost ten years in the Carmel were outwardly undistinguished. Though she yearned to go off to Vietnam to become a missionary, Thérèse died young of intestinal tuberculosis in 1897. When the sisters came, as remains the Carmelite tradition, to compile an obituary of her to circulate to other monasteries, they struggled initially to find anything but platitudes to say about her. It was only when Pauline — by then Mother Agnes and the prioress — remembered that she had set Thérèse the task of writing down her memories of childhood and more recently her thoughts about vocation, that they unearthed the manuscript which was to become Story of a Soul and sell in its tens of millions around the world. In place of an obituary, the Lisieux Carmel had the text of this autobiography printed in book form. After it had been distributed to other convents, there were a few left over, so these were handed out to locals. Soon requests came in for additional copies, and then more and more. The cult of Thérèse was born as a word-of-mouth phenomenon.

The 24 sisters at the Lisieux Carmel rarely give interviews. It is not part of their vocation. And they are equally reluctant to open the doors of their enclosure to many visitors lest it disturb their daily routine of prayer, contemplation and labour (in their case, bookbinding). However, it is a day of celebration when I visit — a sister from Réunion, a French overseas territory in the Indian Ocean, has made her final profession and so Sister Marie Lucille, in her late eighties and able to remember, as a young nun, the last years of Thérèse's sisters at the Carmel, agrees to meet me. 

Bird-like, with pale, almost translucent skin, she wears the modern, cut-down version of the habit that clothes the statue of Thérèse, but still in the same brown and white. She seems genuinely at a loss to know why Thérèse has become such a global figure. "Some people who come here," she suggests, practising the English that she has started to study in recent years, "know very little about her and are attracted, I don't know why, perhaps because she is a woman, or perhaps because they read her book,  Story of a Soul, and as a result they are very in love with her." What is it, though, I press her as we sit in the Carmel's parlour, about the autobiography that chimes so much with the modern reader? "It must be Thérèse's spirituality. The important thing is her love for Jesus and for the simple life, to serve the world. Everybody can understand her book." She says it less as a compliment, I can't help thinking, than as an observation.

Thérèse called her approach to finding God in the everyday the Little Way. "When I read certain treatises," she wrote in Story of a Soul, "where many obstacles to perfection are shown, my poor mind grows tired very quickly. I close the learned book that wearies my head and dries up my heart and I take instead the Holy Scripture. Then everything appears to me in a clear light. A single word opens out infinite horizons to my soul. Perfection seems easy to reach."