Because God told them to.

BBC: A shot of religion in the Holy Land

They went to this church, see, and this preacher told them she was a gift from God.

NEWYORKER: Free Radicals

They were cautioned against alcohol, tobacco, and gum chewing, and were told that they should consider it a miracle of God if any decent man ever wanted to marry them.

NEWYORKER: Stone Mattress