Among a certain circle of art historians, including the BBC broadcaster Andrew Graham-Dixon, is a belief that the Renaissance was ignited by a single spark in the form of one man: St. Francis of Assisi. Born into wealth in Umbria around 1181, Francis abandoned a lavish lifestyle for one of poverty and preaching after experiencing a vision: in his 20s, in a chapel outside of Assisi, while he looked at a painting of the crucifixion, Christ came alive and said, “Repair my church.” Francis subsequently traveled throughout Italy and the Holy Land, establishing the Franciscan Order on the pillars of penury, peace, and environmentalism.

Sandro Botticelli’s Saint Francis of Assisi with Angels, painted in the mid–15th century.

Graham-Dixon argues that the way Francis preached to the illiterate working class—using the Italian vernacular to recount Christ’s humanity and humility—enkindled more realistic, less divine depictions of his body. And by filling that body with muscle, blood, and pathos, artists laid the foundations for the great European art movement.

Dr. Joost Joustra, a co-curator of the exhibition “Saint Francis of Assisi”—which opens at the National Gallery, London, today—thinks there might be a simpler explanation for the friar’s artistic legacy. “He was there to inspire by actions, whether embracing a leper, preaching to birds, or brokering peace with a wolf, and maybe these actions could be translated into images better than text.”

From 1985, Untitled (for Francis), by Antony Gormley.

This, Joustra adds, helps account for why there were, by some estimates, a staggering 20,000 images of Francis made in the century following his death, in 1226, and canonization, just two years later. The show brings together some 40 rousing depictions of Francis that range from 13th-century, gold-ground panel paintings, perhaps made by someone who had actually seen him deliver a sermon, to Caravaggio’s lyrical Baroque portrait of Francis in ecstasy after receiving the stigmata.

Il Sassetta’s Saint Francis Before the Sultan (1437–44).

There are also works by contemporary artists that shine a light on our enduring fascination with Francis. One of them is by the British sculptor Antony Gormley, who attended a boarding school founded by Benedictine monks. His Untitled (for Francis) is a humble lead cast of his own body, but posed as Giovanni Bellini sees Francis in the painting St. Francis in the Desert. Stigmata holes pierce its surface and invite the onlooker to peer inside and imagine what the saint felt when receiving his holy wounds.

The exhibition is sometimes arranged chronologically, examining how artists in certain periods chose to depict Francis. In other places it’s thematic, and looks at Francis’s radical ideas and his relationship with the natural world. Joustra, who’s been flying back and forth to Assisi, says his curatorial decisions have been guided throughout by the Franciscans themselves. “I’ve talked to the friars about the objects they still own, and what Francis means to their world and our world today. There is always something new that they bring to my attention.”

Arthur Boyd’s St. Francis Being Beaten by His Father (1965).

One masterpiece the friars couldn’t help Joustra secure is the late-13th-century cycle of paintings located in the Upper Church of the Basilica of Saint Francis of Assisi. Across 28 scenes, and with great ambition, it spells out the story of Francis’s life and miracles. Its pigment, however, was bound directly to the walls—mostly by the magnificent Giotto, who became the Franciscan Order’s de facto official image-maker. These pictures were pivotal to the development of narrative painting and helped make Francis’s namesake basilica an artistic crucible for the cultural shift that would soon become known as the Renaissance. Not wanting to exclude them from the show, Joustra has had some of the most important sections re-created for the walls of the National Gallery. —Harry Seymour

“Saint Francis of Assisi” is on at the National Gallery, in London, through July 30

Harry Seymour is a London-based art historian and writer