How we cite our quotes: (Act.Scene.Line)
Quote #1
Though some o'th'court hold it presumption
To instruct princes what they ought to do,
It is a noble duty to inform them
What they ought to forsee. (1.1.19-22)
Courtiers, Antonio says, aren't just there for decoration. Although princes like Ferdinand surround themselves with useless sycophants, Antonio wants to be a courtier more like those found in the French court; the kind that actually provide useful advice to their princes, instead of just simpering and fawning.
Quote #2
I am making my will, as 'tis fit princes should […] (1.1.368)
The Duchess says this right before she proposes to Antonio. At the moment she says it this line sound like, "I'm a ruler, so it's important that I write my legal will," but once it's clear that she intends to woo Antonio, it can also sound like "I really want to marry Antonio, and as a prince it's right that I make my desires (my will) a reality." Which is cool, because it makes it sound like it's her duty to marry Antonio, because, hey, she's the boss, and that's how it works.
Quote #3
This is flesh and blood, sir,
'Tis not the figure cut in alabaster
Kneels at my husband's tomb. (1.1.445-47)
The Duchess says this during her wooing scene in Act 1, trying to persuade Antonio that she's a Real Woman, not just his distant ice-queen aristocratic boss. In this line, she's specifically fighting against the belief that woman can only marry once, and that a truly chaste woman is bound to honor her dead husband until her own death.
Think about this, though: the Duchess is always identified by the title she received from her dead husband, and all of her political power—"I am Duchess of Malfi still"—comes from him. What identity do you think the Duchess ultimately embraces more, that of the imperious widow of dead aristocrat, or of the wife of a living, un-aristocratic man?