Jewish ritual: the secret to community?

For communities all over the world, keeping Shabbat is one of the most important parts of what it means to be Jewish. With a never-ending cycle of festivals, traditions and practices, why did Shabbat rituals in particular – from hamotzi to havdalah – become such a defining part of what it means to be Jewish? And why have Jews gone to such great lengths to keep these millenia-old practices going, even in times of danger?