My master being a political demagogue
Brown's characterization of his master as a "political demagogue" compares publicly displayed respectability with private harshness. Individuals who publicly supported leadership and democracy may have secretly supported slavery. This reinforces Brown's criticism of American politics' hypocrisy.
They must be treated as “men-stealers—guilty of the highest kind of theft, and sinners of the first rank.”
By labeling slave owners as “men-stealers,” Brown reframes slavery as a moral and criminal act rather than a legal institution. This positions slaveholders not as respectable citizens but as the most serious kind of sinners. This reversal challenges the moral authority of those who justified slavery through law or religion.
A sister has been given up to the irresponsible control of the pale-faced oppressor. This nation looks on approvingly. The American Union sanctions the deed. The Constitution shields the criminals.
Brown's wording here moves from a personal level to a national level on purpose. Beginning with the violation of "a sister" and finishing with the Constitution, he shows how responsibility moves from an individual oppressor to the power of the government. The phrase "pale-faced oppressor" makes authority seem racist, and the words "sanctions" and "shields" show that the American law system was involved in slavery and not just watching.