Which major religion followed by only one group of people

Judaism

Explanation:

Judaism is one o major religion that can only followed by people with Jewish Ancestry. Unlike most other religion, people can't just follow Judaism based on personal faith.

Those without Jewish ancestry technically can still adopt Judaism as their religion. But, they will have to undergone a process called Denomination in which another Jewish will sponsor that person and transition him/her into a community. But not all Jewish community acknowledge the viability of this process

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