The moral of Saint Joan
Ha, ha! I was no beauty: I was always a rough one: a regular soldier. I might almost as well have been a man. Pity I wasn't: I should not have bothered you all so much then. But my head was in the skies; and the glory of God was upon me; and, man or woman, I should have bothered you as long as your noses were in the mud. Now tell me what has happened since you wise men knew no better than to make a heap of cinders of me?
Why does Shaw write an epilogue?
An epilogue is an extra piece that happens after the main action of a play or story. This extract is from the epilogue to the play. The main part of the play came to an appropriate climax with the burning of Joan at the stake for being a heretic. Shaw could have ended the play at that point.
However, had that been all that there was to the story of Joan, we would not remember her today in the way that we do.
The whole power of her story is in the reversal of her fortunes. She was burnt at the stake as a witch, but this judgment was then reversed and many centuries later, she was recognised as a Saint.
The epilogue allows Shaw to include all this in the story of Joan.