'Tis the season of the Christmas pageant. In churches across the country, troupes of pint-size actors are assembling, wearing costumes made of bedsheets cinched with rope belts and taking the stage to re-enact an ancient, sacred story: the birth of Jesus.

The religious pageant, that peculiar intersection of liturgy and theater, traces its roots to the Middle Ages. Christian clerics in Europe introduced drama into the Mass (a dramatic event in its own right) as early as the ninth century to enrich the faith and understanding of worshipers. Over time these performances evolved into cycles of plays that told the whole salvation story, from the fall of humankind to the nativity to judgment day.