When the wind changes directions on the banks of the Loire, Dunois is convinced that it's a miracle. He's sure that Joan has been sent by God. To him it's symbolic of God's blessing on Joan. It could also be seen as having a greater symbolism. Joan's presence will change the direction the war is going. It's also a change for Joan herself. She goes from talking about taking back France to actually doing something about it. When the wind changes, so will her life, so will France, so will history.
The fact that Joan's heart doesn't burn can be seen as symbolic. The undamaged heart could represent her eternal spirit, which doesn't die along with her body. Her memory lives on to inspire many more generations to come. The play recognizes this in the epilogue, when the Gentleman comes from the future to tell us that Joan has been made a saint. Like Christ, Joan is resurrected in a sense by her canonization. Of course, this is a Shavian play, so no triumph comes without a twist of irony. The epilogue hypothesizes that, if she did come back to life literally, as is said of Jesus, that she would just be burnt all over again. Perhaps, the spirit that her unburned heart symbolizes is all the world ever really needed or wanted from her.
The very first scene starts off with Robert de Baudricourt brow beating his poor Steward because there aren't any eggs. We can understand. We also get grumpy when there's no breakfast. The hens haven't been laying ever since Robert refused to see Joan. The scene ends with Robert giving in and supplying Joan with the soldiers and supplies she needs to go see the Dauphin. Immediately, the hens start laying again. Is this just complete randomness on Shaw's part or is it incredibly symbolic? Let us examine:
Eggs are an ancient symbol of birth and renewal. It seems pretty logical, right? Eggs=little baby birds=birth. This symbolism goes all the way back before the Romans and Greeks.
It's so old that nobody even knows where it came from. Ever heard of an Easter egg? Ever wondered what they have to do with Jesus being resurrected? It comes from when the Catholic Church was going around converting all the pagans. "Pagan" is the term Catholics made up for any and all of the indigenous religions they came into contact with. Pagan basically meant you weren't Catholic. Anyway, the pagans had lots of holiday traditions that they were pretty reluctant to give up – one of which was celebrating the spring equinox with eggs. Get it? Eggs=little baby birds=birth=spring.
The Catholic priests found that it was a lot easier to convert people if they let them hold on to a few of their old traditions. They were like: "OK, you can still have your spring festival and your symbolic eggs, but we're going to celebrate Jesus' resurrection now instead of the renewal of the earth." (Incidentally the word Easter comes from the Saxon goddess Eastre.) The pagans were cool with this switcharoo. So, now we have: eggs=little baby birds=birth=Jesus' resurrection. (You can learn more about Easter here.)
When Robert decides to help Joan begin her quest, it's a birth of a sort. Only, instead of a fuzzy little chick, a saint is born. The symbolism is doubly meaningful because Joan is a Christ figure. She ends up being martyred just like Jesus and even resurrected in a way when she is made into a saint. OK, so the final equation is: eggs=little baby birds=birth=Jesus' resurrection=Saint Joan of Arc.
Joan as Nationalism
You may ask, what is this Nationalism of which you speak? We'll let Bishop Cauchon explain: "I can express it only by such phrases as France for the French, England for the English, Italy for the Italians, Spain for the Spanish, and so forth" (4.120).
This may not seem like such a radical idea today, but back then it was crazy talk. During Joan's time, people that mostly spoke French and lived in a land referred to as France didn't necessarily call themselves French. If you zoomed back in time and asked your average French speaking peasant where they came from, they might say Normandy or Aquitaine, but never France. The land was divided among lots of smaller duchies and fiefs. People were more loyal to their feudal lord than the king. In Shaw's play we see Joan burst onto the scene with a new philosophy. She thinks that all these people going around speaking French ought to be united under a strong French king.
Joan comes to symbolize this new Nationalism, and as a result she terrifies the feudal lords, French and English alike. The Earl of Warwick will elucidate us as to why: "Men cannot serve two masters. If this cant of serving their country once takes hold of them, goodbye to the authority of their feudal lords" (4.19). He goes on to say, " If the people's thoughts and hearts were turned to the king, and their lords became only the king's servants in their eyes, the king could break us across his knee one by one; and then what should we be but liveried courtiers in his halls?" (4.112).
This is exactly what happens in the future. If you want a good example, watch Henry VIII on The Tudors; you'll see the absolute power that future monarchs hold. Eventually the feudal lords become exactly what Warwick describes, only the king's servants. When Warwick orchestrates Joan's execution, in his mind, he's burning a symbol of this new Nationalism that threatens his power.
Note: It should be recognized that Shaw's use of the word Nationalism, is anachronistic, meaning that it is out of place in this time period. The term didn't come into use for several centuries after Joan's death. Shaw says in his preface that he chose to do this to better help modern audiences understand the play.
Joan as Protestantism
At Joan's trial, Bishop Cauchon tells everybody that, "The mighty structure of Catholic Christendom […] may be […] brought to barbarous ruin and desolation, by this arch heresy […] Protestantism" (6.74). But what exactly is Protestantism and why is it so dangerous to the Church? Warwick gives a good definition, saying "It is the protest of the individual soul against the interference of priest or peer between the private man and his God" (4.117).
Basically, Protestants in this novel believe that they should be able to talk to God themselves rather than having a priest do it for them. You can probably understand why the priests might not be fans of this idea. If everybody goes around communing with God on their own, won't all the clergy lose their job? Cauchon and his peers feel this is very dangerous because your average everyday Joe doesn't know enough to interpret God's will. They think it takes a trained and educated Churchman to get it right. For example, how is a layman supposed to know the difference between God's voice and Satan's?
Joan, of course, thinks she has every right to commune with higher powers on her own. She claims to the very end that her voices are sent from God, despite the fact that the Church tells her that they're demonic in origin. Joan even goes so far as to say, "I know that your counsel is of the devil, and that mine is of God" (6.233). Whoa, that's a harsh accusation. Not only is she claiming their interpretation is wrong, but also that it's been influenced by the Devil.
What's ironic is that Joan doesn't start out as a rebel against the Church at all. When she first meets the Archbishop at Charles's court she is extremely reverent, so much so that the nobles make fun of her. Even for most of her trial she is generally respectful of the Church as an institution. Nevertheless, her faith in her own interpretation of her voices over the Church's brands her as a heretic. The Church sends her to the flames because they can't allow this symbol of Protestantism to survive.
Note: Once again we have an anachronism. The word "Protestant" didn't come into popular use until Martin Luther's Protestant Reformation in the 1500s. Shaw, of course, is well aware of this, and chose to include the term its modern implications.