As nineteenth-century poems go, this certainly isn’t the toughest thing you’re going to encounter. It’s pretty conversational – in fact, it’s half of a conversation. You can easily imagine that you’re the servant sitting in the Duke’s private gallery, listening to him talk about when and how the portrait was painted and what makes him such a jealous psychopath. The most difficult thing about the poem is the syntax, the order of words and phrases that the Duke uses. For example:
"Frà Pandolf" by design, for never read
Strangers like you that pictured countenance,
The depth and passion of its earnest glance,
But to myself they turned (since none puts by
The curtain I have drawn for you, but I)
And seemed as they would ask me, if they durst,
How such a glance came there; so, not the first
Are you to turn and ask thus. (5-13)
We count nine different phrases and clauses in that nine-line sentence, including the parenthetical aside, just so the Duke can say, "I brought up that guy Pandolf on purpose, because people always want to ask me who painted the picture." Passages like this are especially strange because the Duke can be concise and to the point when he wants to be: "This grew; I gave commands; / Then all smiles stopped together" (45-46). That’s the shortest way of saying "So, her behavior became even more extreme, and I decided that I would have her murdered" that we’ve ever heard.
Why so much variation in the length and complexity of the sentences? Well, for one thing, it makes the poem more interesting than if every sentence was exactly one or two lines long. But it also lets us gauge the Duke’s mood and mania. In the shorter sentences where the Duke is to the point, we can imagine him being steely and strong: "I gave commands." No compromises there. But in the longer, more tortured sentences with wacky syntax, we might wonder exactly why it’s so hard for him to say these particular things in a straightforward way, and what other details are creeping into the sentence that don’t need to be there.
In the long passage we quoted above, what the Duke is trying to say is just "People always ask me who painted the picture and how they made it so lifelike," but he ends up also mentioning that he insists on having total control over the painting. Our point is that, when this poem gets difficult to understand, that’s when you should start looking for several levels of information coming from the Duke – the things he’s trying to say, the things he lets slip on purpose, and the things he lets slip by accident.