Religion is a human phenomenon met in every culture, where spiritual beings are thought to be the causes of life, of the appearance of universe and of many natural changes. But why do people believe all these things? This article presents shortly the answers given to this fundamental question: religion is a social product; faith exists thanks to our psychic stock liable to believe or could be a consequence of the cultural indoctrination. The author refers to Mircea Eliade which succeeded in reconciling sacred with profane, underlining the ontological complementarity that unifies them. But the author does not stop at the theoretic aspects; he also suggests the necessity of a personal and faithful answer in front of the challenge of confessing clearly and of defending the contents of our faith.