The difference between miracles and human feats is a motif in the play. One instance when it comes into play is in Scene 5, when Dunois insists to Charles that it was his own hard work, more than Joan's voices, that has brought the king victory:
Do not think, any of you, that these victories of ours were won without generalship. King Charles: you have said no word in your proclamations of my part in this campaign; and I make no complaint of that; for the people will run after The Maid and her miracles and not after the Bastard’s hard work finding troops for her and feeding them.
Dunois feels deprived of due credit because everyone is so enamored of Joan. "The Maid and her miracles" are a more compelling theory for France's success than "The Bastard's hard work finding troops for her and feeding them." If Joan and her "miracles" are responsible, that means that France was divinely selected to prevail against England in this war. But, Dunois points out, the "miracles" would have been impossible without his military leadership.
In Shaw's play, both things are true. Shaw does not particularly believe in miracles and includes numerous speeches about how anything can look like a miracle if people don't understand how it happened. For example, in Scene 2, the Archbishop explains that a miracle is an event that creates faith. He goes on to make a muddled distinction between miracles and fraud, suggesting that the Church might not distinguish very well between the two. At the same time, the troops' belief that Joan can bring about miracles has inspired them to fight well. Dunois's hard work is to be credited for France's victory, but the hard work would have been for nought if not for Joan. The two of them have worked well together. Shaw seems to agree with the Archbishop that miracles are "real" insofar as people believe in them, and he seems to think that even deceptive miracles can be useful in some circumstances. Wherever the inspiration is coming from, the idea of miracles can help push people to accomplish incredible things.
