religious fervor

Religious fervor is intense, passionate devotion to one's faith—the kind of zeal that drives deep commitment to religious practice, belief, or cause.

The phrase often describes enthusiasm that goes beyond ordinary observance: She spoke about her conversion with religious fervor.

It can appear admiringly or with a note of concern, depending on whether the speaker sees such intensity as inspiring or excessive.

By extension, fervor applied to secular pursuits may be called religious: He approaches fitness with religious fervor.