Also, related, a recent article by Gerard Russell in the Washington Post: The Middle East is full of ancient, mysterious religious sects. The Islamic State is wiping them out.. Excerpt:
Yazidis like Mirza don’t know even the basic tenets of their faith. These groups’ holy books are carefully hidden from lay people; the priests who read them must promise never to reveal their contents. Entering these leadership ranks isn’t easy, either. Among the Mandaeans of southern Iraq, for example, a people who revere John the Baptist and believe in a colorful array of demons and planetary angels, a would-be priest must spend seven days without food or sleep.Background here and links.
There are at least half a dozen groups in the Middle East which follow this code of secrecy. Their adherents number more than 5 million in Syria, Lebanon, Israel and Iraq. They include Syrian president Bashar al-Assad’s Alawite sect, and also the Yazidis.