Emile Durkheim, a foundational sociologist, introduced the concept of the sacred as a social construct that signifies things set apart from the ordinary, which can be both religious and secular. His theory argues that the sacred helps create social solidarity and maintain order within communities while being a representation of shared societal beliefs. Despite its influence, Durkheim's broad definition of religion and focus on functionalism have faced criticism for not adequately addressing the complexity and diversity of religious experiences.