People become a member of a religion by baptism in other countries, while those who worship a god of a religion are deemed to be a believer of that religion in Japan, (where many people are shrine parishioners and Buddhist parishioners at the same time).
他国では洗礼を受けた時点でその宗教の信者に成るのに対し、日本ではその宗教の神を拝めば信者とみなす（氏子であり檀家でもある者などが多くいる）。