The Origins of Theatre
The origin of theatre, I am inclined to believe, lies with the cultural necessity to convey religious messages. In many primitive theaters—most notably the Greek theatre—drama would have a ritualistic backbone that sought to honor deities and explain the otherwise inexplicable. Theatre may also have employed religion in much the same sense as it today—as a method of bringing a cultural or community together. When a community is brought together by something as homogenizing and certain as religion, it provides a known structure for events that may seek to do the same. By building off of a known commonality, the theatre could have greater foundation and certainty to its reception.
It makes logical sense, for the birth of a theatre—an event dependent upon a united community—to be structured on a similarly dependent idea. Once the concept of theatrical storytelling established itself, it was able to grow from there and evolve, branching out from ritual and religion.
Even today, in my own experience, the production of theatre is still dependent on the interest and support of a community. The objective of theatre is not only to entertain an audience but to unite an audience in the ideas presented and the moral lessons implied—much akin the religious, fable-like stories that first saw the birth of theatre.