"My Last Duchess" is all about power: the political and social power wielded by the speaker (the Duke) and his attempt to control the domestic sphere (his marriage) in the same way that he rules his lands. He rules with an iron fist. The Duke views everything that he possesses and everyone with whom he interacts as an opportunity to expand his power base. Wives need to be dominated; servants need to understand his authority; and fancy objects in his art gallery display his influence to the world – if he decides to show them. Kindness, joy, and emotion are all threats to his tyrannical power.
The Duke of Ferrara sets himself up to have his power threatened, because he never communicates directly with people about his expectations for their behavior.
In "My Last Duchess," choices about what to communicate and what to withhold are the means by which power is wielded. The Duke sees communicating openly and honestly with someone about the problems you have with their behavior as impossible because it would compromise his authority. It’s also possible to hint at his power by intentionally letting stories of the past exploits slip to a new listener. However, because language is full of subtlety, the Duke might accidentally communicate more than he meant to about his own psychosis.
The Duke is only able to describe his maniacal feelings to someone who is not the object of those feelings.
"My Last Duchess" is a piece of art about a piece of (fictional) art – a poem about a pretend painting. The speaker of the poem, the Duke of Ferrara, is a connoisseur and collector of objets d’art, or art objects, which he displays privately in order to impress people. In this poem, art and culture become tools for demonstrating social status – and ways to reduce unstable elements, like the Duchess herself, to things that can be physically controlled.
Even though the Duke is a collector of art objects, he doesn’t really appreciate them; he only cares about the way they increase his status and demonstrate his power.
In "My Last Duchess," a husband murders his wife because she blushes and smiles at other people – even though theses blushes are out of her control and probably entirely innocent. This is pretty much the textbook definition of an abusive, controlling husband. The Duke doesn’t even want his wife to thank people for gifts, because it makes him jealous. But we think this goes beyond abuse into the realm of madness: after all, trying to control someone is abuse; thinking that because someone blushes she must be having an affair, and that the only remedy is murder is just insane.
The Duke’s obsession with totalitarian power, and his tendency to punish innocent or nearly innocent behavior with the most extreme penalties, make it clear that he’s a psychopath.
The Duke in "My Last Duchess" is pretty much the green-eyed monster incarnate. He’s almost an allegorical figure for jealousy. He’s jealous of the attention his wife shows to other people – even if all she does is thank them for bringing her some cherries. He’s jealous of every smile and every blush that she bestows, intentionally or unintentionally, on someone else. He’s so jealous that he can’t even bring himself to talk to her about her behavior – murder is the only solution he can come up with. His jealousy isn’t just about romantic attention; it’s about any kind of attention.
The Duke is jealous of the way the Duchess treats other people, not because he loves her and wants all her love for himself, but because he wants her to acknowledge his power over her.