Saint-Pierre will be radically unlike Le Corbusier's other churches and unique among religious structures. Its geometry is produced by the projection of a circle onto a square, a metamorphosis that represented for the architect the transition from the earthly to the spiritual realm and one made possible by a complex hyperboloid shell enclosure. The square base of the church containing functional rooms is surmounted by an enormous truncated cone housing the sanctuary, which is lit by an array of protruding "light cannons." The shell, and the winding pathway into and through the sacred space - another version of Le Corbusier's "promenade architecturale" - are the central elements of Saint-Pierre.

Oubrerie did not attempt to explain the building's symbolic associations. "I am too close to the nuts and bolts to be poetic," he said. "I leave that to others, like my younger colleagues." They point out that the church resembles a nuclear cooling tower, or maybe one of those volcanoes seen on Volvic water bottles. Both may have influenced Le Corbusier. Other people refer to it as the seau à charbon, the coal bucket, a signifier linked to Firminy's industrial past. Interpretation is encouraged by the fact that Saint-Pierre is cast almost entirely in concrete, a material Le Corbusier preferred in his later years for its economy and plasticity.