Joan repeatedly demonstrates herself to be naively earnest, accidentally cultivating her ethos as a good leader by using unrealistically optimistic logos. One instance occurs in Scene 1, when Joan argues in favor of French nationalism:
JOAN. I do not understand that a bit. We are all subject to the King of Heaven; and He gave us our countries and our languages, and meant us to keep to them. If it were not so it would be murder to kill an Englishman in battle; and you, squire, would be in great danger of hell fire. You must not think about your duty to your feudal lord, but about your duty to God.
POULENGEY. It’s no use, Robert: she can choke you like that every time.
Nationalism in the modern sense was a fairly new idea in the 15th century; people tended to have more localized loyalties. Robert de Baudricourt has been telling Joan that soldiers are subject to the will of their feudal lord, and that they do not care whether their lord is from England, Burgundy, or France. Joan refutes this idea by telling Robert that she doesn't understand. She claims that everyone is ultimately a subject of "the King of Heaven," or God, and that God has determined what country and what language everyone will be born into. She takes as a given that the war Robert is waging against the English is just, and she tells him that if there were no divine distinctions between English people and French people, this could not be the case. Otherwise, the death of every English soldier would constitute murder. There is no way Robert is damning himself to eternity in hell by leading his troops against the English. Loyalty to feudal lords, she claims, comes only after the loyalty to king that is dictated by loyalty to God.
Poulengey is impressed with Joan's infallible logic. Part of what makes it so convincing is that she is so earnest: she really seems to believe in God so deeply that she can't see the logic of the petty feudal politics in which Robert has been immersed his whole life. Far from making her seem unfit to lead, Joan's naivety turns her into the nationalist visionary France needs to win the war. It is important to note that Shaw is introducing Joan's argument in favor of nationalism to an early 20th-century audience. The play does not fully buy into Joan's religious fervor, but it does look favorably on her as a visionary leader who is committed to her beliefs. Shaw is dabbling in the idea that fervent nationalism is natural and good—an idea that was popular in this time period and which led to a great deal of terror and genocide over the next several decades.
