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.