'Priests Of Psi, The ' by Frank Herbert

In a future society where trained telepaths form a powerful religious caste that polices and sanctifies psychic abilities, an outsider challenges their monopoly on truth and control, exposing how ritual and secrecy are used to maintain authority; the confrontation forces a reckoning over the ethics of psychic power, the conflict between faith and reason, and the consequences of concentrating mental influence in the hands of a privileged few.