The symbolism of the Crèche, or Nativity Scene is obvious, but It has an interesting history.
It is believed that St. Francis of Assisi and his monks were the first to use a nativity scene in a Christmas celebration.  People dressed up and played the parts of Mary, Joseph, the Magi and the shepherds.  Live animals were also included in the scene.  By tradition, there was never any dialog, just pantomime.  The idea became popular and spread throughout Europe.  Over the centuries, statues and paintings gradually replaced the living representatives.  In recent years, some churches have begun to re-establish the living crèche concept.