The speaker initiates his control and power over his last duchess by using the possessive pronoun "my"
The readers interest is engaged by wondering why this is his "last" duchess, and wonders what happened to her.
“I call that a piece of wonder”
Is quite ominous because is suggests that the Duke sees his dead wife as a piece of art and a possession to be owned, like an object, objectifying his dead wife, showing the power he has over her, even after her death
“Will’t please you sit and look at her?"
The rhetorical question inviting the guest to sit and look does not require a reply implying it is more of a command than an optional invitation, which adds to his controlling and powerful nature
"But to myself they turned (since none puts by the curtain I have drawn for you"
This section of the poem reveals more about the Duke’s controlling nature
By covering the painting with the curtain, the Duke is able to control who sees her in death in a way he could not in life
This behavior is sinister and the reader begins to wonder if he was involved in her death, perhaps covering the painting as a symptom of his guilt