Which type of religious organization claims to include almost all members of a society?

The type of religious organization that claims to include almost all members of a society is an ecclesia. Ecclesiae are characterized by their integration into the broader social and political fabric of a society, often being the established, state-supported form of religion. They tend to have a large following, encompassing a significant portion of the population, and they often play a major role in the cultural and societal norms of the community.

In an ecclesia, membership is usually not a matter of personal choice but seen as part of one's identity within the society, often linked to national or ethnic identity. This stands in contrast to denominations, which may represent specific sects within a broader religious tradition but do not encompass the entire society. Likewise, cults and new religious movements are typically smaller, often emerging in response to modern social changes, and do not claim to include the entire society.

Thus, ecclesiae hold a unique position in the study of religious organizations, being the type that integrates seamlessly into the societal structure and claims membership from almost all individuals in that society.