St. Therese of Lisieux (1873–1897) is one of the most popular saints in modern times. What makes her life so outstanding and such an inspiration to so many people?
She had no sustained spiritual visions, unlike St. Bernadette of Soubirous before her or the three children of Fátima after her. She had no stigmata, was not a martyr, was not a teacher during her lifetime, and did not start a religious order.
Her life was sealed off, as it were, from the rest of the world in a cloistered convent. How did she become so well-beloved around the world?