Druze teaching holds taqammus: at death the soul passes immediately into a body being born, without interval, judgement scene or waiting place. The number of souls was fixed at creation and does not change, so the same souls circulate through successive lives, and a Druze soul is always born into a Druze body.
That doctrine does more work than any other in the tradition, because the community's social structure follows from it. If the roster of souls is closed, conversion into the faith is not forbidden so much as meaningless: one cannot join a set one was not created within. Conversion out is equally incoherent in the community's own terms. Marriage outside the community is a grave matter for the same reason, and Druze practice is strictly endogamous. The whole architecture of closure that outsiders describe as secrecy or exclusivity is, from the inside, a straightforward consequence of a metaphysical claim.
It also shapes the emotional texture of Druze life. Death is met with a composure that visitors regularly remark on, because it is a transition rather than an ending, and funerals are not organised around despair. Children who report memories of a previous life are taken seriously rather than hushed, and such reports have been collected and studied by outside researchers, who have found the Druze among the most productive communities for the purpose precisely because the belief makes families willing to talk.
The door closed at a datable moment. Preaching began in 1017 under the Fatimid caliph al-Hakim; the call was suspended and then formally closed in 1043 by al-Muqtana Baha al-Din, and no new adherent has been admitted since. Nearly a thousand years of a religion that has taken in nobody explains its demography: something near a million Druze, concentrated in Lebanon, Syria, Israel and Jordan, with substantial diaspora communities in Venezuela, the United States, Australia and West Africa.