Built between 1163 and 1345, vandalized during the French Revolution and completely renovated in the mid-19th century, the world’s most famous Gothic cathedral—and arguably the world’s single most famous church—had been through a lot even before a devastating fire tore through it in April 2019, destroying much of the roof and causing its 19th-century flèche, or spire, to topple.

Once the flames had been extinguished (the cause of the fire is still unknown), donations poured in from all over the world and Emmanuel Macron, France’s president, vowed to rebuild.

Just over five-and-a-half years later, Notre-Dame flung open its portals last week with a dose of pomp and national pride that rivaled this summer’s Olympic Games held in Paris.

Restoring the church to its pre-conflagration state has required 2,000 freshly felled oak trees, over 35,000 cubic feet of limestone and 43,000 square feet of lead. The scale of the work that has been done is mind-boggling, employing roughly 2,000 workers and craftsmen—among them master carpenters and stonemasons, bellmakers, stained-glass artists and painting restorers—for a task “ad maiorem Dei gloriam inque hominum salutem” (“for the greater glory of God and the salvation of humanity”). Under the general direction of Philippe Villeneuve, the chief architect overseeing France’s historic monuments, Gen. Jean-Louis Georgelin, head of the reconstruction task force until his death last year, and his successor, the engineer Philippe Jost, the army of workers and artisans stabilized the building and restored dozens of gargoyles, chimeras and copper statues, 22 altars, over 300 feet of ornate woodwork, and much else. Price tag: about $900 million, which was easily raised from donors in France, America and the world over. It takes a nation—and some friends.

View of the nave during Mass. Photo: christian hartmann/Reuters

Entering Notre-Dame on Monday, as dusk fell on Paris hours before evening Mass, I was jolted by the shock of the familiar and the unfamiliar. It is unmistakably the same awe-inspiring sanctuary I have set foot in numerous times over the past quarter-century, most recently in late March 2019, mere weeks before the fire. Yet the soaring nave, flanked by double lateral aisles that make Notre-Dame one of the widest of Gothic cathedrals, also makes an entirely new impression. Cleaners and restorers have scrubbed every inch of the cavernous structure. From the luminous marble floor, with its checkerboard pattern, to the squat circular marble columns, up past the arches to the sexpartite vaults, the entire vessel is startlingly, brilliantly bright.

It takes some time for your eyes to adjust. Darkness, after all, was formerly so integral to old Notre-Dame’s unique atmosphere. (In fact, in the mid-18th century, clergy who were fed up with the lack of light tried to remedy the situation by removing the cathedral’s medieval stained-glass windows. Fortunately they left the three rosettes.) Advancing to the transept—the arms of the cruciform church—through the north aisle, with its seven chapels depicting Old Testament figures, I found myself acclimating to my pristine stone surroundings with every passing step. The cathedral’s aged and weathered patina is gone and I’m sure that some will mourn the loss. But now it hums with renewed vitality.

One of the rose windows. Photo: Gao Jing/Zuma Press

Everywhere you look, there’s another revelation. The polished and restored chandeliers under the supporting arches of the nave provide a subdued glow. Spotlighting illuminates the clerestory and chapels and allows one to appreciate the ceiling as never before; the restored painted oculi in the center of the vaults pop out with surprising vibrancy. The famous rose windows mercifully survived the fire. They’ve been meticulously cleaned: Even as evening descended, one could admire their kaleidoscopic intricacy. Past the new bronze altar designed by Guillaume Bardet—one of the very few contemporary interventions in the interior—in the heart of the transept, the choir stalls with their ornate carvings have been delicately reconstructed with trees donated from private forests throughout France. The murals in the radiating chapels of the ambulatory, which is the oldest part of the cathedral, were largely painted or restored in the 19th century. Even prior to the great fire, some of these polychrome rooms, romantic imaginings of the medieval past, bordered on kitsch. Now the colors seem almost cartoonish, but there’s no doubting the skill of the restorers. One of these chapels preserves the metal statue of the rooster—one of the symbols of France—that perched upon the spire that plummeted when it was engulfed in flames and is dedicated “to the women and men who saved and raised Notre-Dame de Paris.”

The high altar and a new tabernacle designed by Guillaume Bardet. Photo: julien de rosa/Agence France-Presse/Getty Images

It seems impossible to overstate how Herculean their task has been or how profound their contributions. And that’s not even considering the structural renovations that have been made, including the complete reconstruction of the wooden medieval attic known as “la forêt,” that are largely out of view.

I took my seat for Mass. As the strong chords of the restored great organ, its 8,000 pipes painstakingly cleaned, resounded and echoed through the cathedral, this magnificent edifice, as much a temple to God as it is to human ingenuity and industry, felt reborn.

—Mr. Goldmann writes about European arts and culture.