Wikipedia describes pareidolia as follows:

Pareidolia (pronounced /pærɪˈdoʊliə/ pa-ri-DOE-lee-ə) is a psychological phenomenon involving a vague and random stimulus (often an image or sound) being perceived as significant. Common examples include seeing images of animals or faces in clouds, the man in the moon, and hearing hidden messages on records played in reverse. The word comes from the Greek para- ("beside", "with", or "alongside"—meaning, in this context, something faulty or wrong (as in paraphasia, disordered speech)) and eidolon ("image"; the diminutive of eidos ("image", "form", "shape")). Pareidolia is a type of apophenia (a tendency to create patterns where none exist).

Carl Sagan hypothesized that as a survival technique, human beings are "hard-wired" from birth to identify the human face. This allows people to use only minimal details to recognize faces from a distance and in poor visibility but can also lead them to interpret random images or patterns of light and shade as being faces.

Most people recognize illusions for what they are, but some become fixated on the reality of their perception and turn an illusion into a delusion. A little bit of critical thinking, however,  should convince most reasonable people that a burnt area on a tortilla that looks like Jesus are accidents and without significance.