Tragedy and Comedy are classic symbols of theatre and metaphors for the duality of human emotional experience. Like Yin and Yang, they exist within each other.
The theatrical masks of classic Greece, Tragedy, and Comedy were used in their sacred dramas; actors in the early drama were not meant to show their faces; instead, bronze or leather masks were held up to illustrate the right emotions for the course of the story/play.
All around the world, and in contemporary indigenous cultures, masks are meant to display the attributes of the deities and to tell sacred stories, such as the use of masks in Hindu Bali. Masks are often regarded as a vessel for the Gods to enter this order of existence, indwelling or possessing the actor/dancer during the duration of the ritual drama. The old German word for the mask was "grim," which also occurred in the names of deities and heroes, hence the idea that the divine beings were also literally indwelling in some measure in the masks. The church may have been fearful that the old pagan gods would thus manifest again and forbade the wearing of masks. However, the practice persisted in celebrations of Halloween and Carnival, among mummer troupes, and in-country festivals that still honored such archetypal beings as the Green man.