Patriotism is a main theme in the story: Webster claims that the Devil cannot take the soul because he cannot claim American citizenship. "And who with better right?" the devil replies, going on to list several wrongs done in the US, thereby demonstrating his presence in the US. The Devil says "I am merely an honest American like yourself — and of the best descent — for, to tell the truth, Mr. Webster, though I don't like to boast of it, my name is older in this country than yours."
Webster insists on a jury trial as an American right, with Americans for the jury and an American judge. The Devil then provides the worst (from Webster's perspective) examples of Americans for the judge and jury. In Daniel's speech "He was talking about the things that make a country a country, and a man a man" rather than legal points of the case. For Webster, freedom and independence defines manhood: "Yes, even in hell, if a man was a man, you'd know it."
This theme of American patriotism, freedom and independence is the explanation for Webster's victory: the jury is damned to hell, but they are American and therefore so independent that they can resist the Devil. However, in reality many of the jury would not have classed themselves as Americans, as Governor Dale, Morton, Hathorne, and Blackbeard were English, and King Phillip was a Wampanoag. Butler and Girty would have called themselves Americans – and indeed were Americans – but they were loyalists, and Webster might not have intended any but U.S. citizens. Classifying the jurors as "Americans" involves a wider definition, including all who had a part in its history – even those who lived and died as English people before 1775, the Loyalists who actively opposed the creation of the US, and even the Native Americans who altogether opposed European settlement.
In his speech, Webster denounces slavery. "And when he talked of those enslaved, and the sorrows of slavery, his voice got like a big bell." Benét acknowledges the evil by having the devil say: "When the first wrong was done to the first Indian, I was there. When the first slaver put out for the Congo, I stood on her deck." As for Webster, "He admitted all the wrong that had ever been done. But he showed how, out of the wrong and the right, the suffering and the starvations, something new had come. And everybody had played a part in it, even the traitors."
The real Daniel Webster was willing to compromise on slavery in favor of keeping the Union together, disappointing many abolitionists.
Treatment of the Indians
The story may be seen as ambivalent on the treatment of the Indians/Native Americans. Webster states "If two New Hampshiremen aren't a match for the devil, we might as well give the country back to the Indians." However, the stranger/Satan remarks that "When the first wrong was done to the first Indian, I was there", which implies the author's acknowledgement that the Indians were wronged. Yet "King Philip, wild and proud as he had been in life, with the great gash in his head that gave him his death wound" is included among notorious villains of American history – even though more modern historical sentiment holds that King Philip's "villainies" were merely a just response to the wrongs done to his people.
(As an aside, the historical King Philip died from a gunshot to the heart and not a gash to the head.)
Yet later on, Daniel Webster's appeal to the jury on "what it means to be American" specifically includes King Philip among "the Americans". This is an anachronism as the historical Daniel Webster would have been unlikely to express such an opinion. The narrator also expresses sympathy for King Philip when he tells us that one juror "heard the cry of his lost nation" in Webster's eloquent appeal.
These ambiguities probably reflect ambivalent perceptions of this aspect of American history at the time of writing rather than at the time when the story is supposed to take place.
The devil is portrayed as polite and refined. When the devil arrives he is described as "a soft-spoken, dark-dressed stranger", who "drove up in a handsome buggy". The names in this story for the devil (Mr. Scratch, or the stranger) are both terms that were locally used around New England and other parts of the pre-Civil-War United States. (For example, "Perhaps Scratch will do for the evening. I’m often called that in these regions.") These terms are taken primarily from the Washington Irving story published more than 100 years before, "The Devil and Tom Walker".