When Gaudí took over the direction of the construction of the temple, only the crypt had begun to be erected. In this section, he made modifications to the capitals, transforming them from their initial Corinthian style to a new style inspired by vegetal elements. Gaudí progressed from his early neo-Gothic approach to his signature style, characterized by a naturalistic and organic approach, influenced by nature itself. The architect argued that Gothic was deficient because its straight lines and system of pillars and flying buttresses did not align with the laws of nature. For Gaudí, nature tended to adopt regular geometric forms, such as the hyperbolic paraboloid, the hyperboloid, the helicoid and the conoid.

These regular shapes are generated by a straight line called the "generatrix", which moves along one or more lines called "guidelines". Gaudí found a profusion of these forms in nature, as in reeds, canes or bones. For him, there was no structure superior to that of a tree trunk or human skeleton. These forms were both functional and aesthetic, and Gaudí applied them ingeniously, adapting natural language to the structural forms of architecture. Gaudí related the helical form to movement and the hyperboloidal to light. About regular surfaces, he said: "Paraboloids, hyperboloids and helicoids, by continuously varying the incidence of light, present an intrinsic richness of nuances that make ornamentation and even modeling superfluous".