Arranged marriage
To strengthen their family's power, Lucrezia de'Medici's mother and father decide to arrange a marriage to Alfonso II d'Este, the Duke of Ferrara (and head of the second most powerful family in Renaissance Italy). Typically, people marry each other because they love each other, not for political purposes. And though, in many instances, those in arranged marriages love each other, Lucrezia and Alfonso II d'Este don't love each other. Their marriage reflects a harsh reality: sometimes, married people (including those in arranged marriages) don't love each other. Lucrezia's brave and dangerous decision to leave her loveless and oppressive marriage also shows that people can do something to exit a marriage in that they don't feel cherished and loved.
The nature of power
The nature of power is another significant theme in The Marriage Portrait. Lucrezia comes from an influential family interested only in increasing their capacity. Her family likewise associates themselves only with the powerful; they look down on commoners who can't help them in any way. The novel makes the point that people with power scarcely want to give it up, invariably want to accumulate more power, and frequently look down upon those who don't have the ability. And as with the de'Medici family, those with power are often not good people.
Art
Lucrezia was fascinated with art for much of her life and dreamed of becoming an artist. However, she never took steps to become an artist because her family constrained her. After Lucrezia leaves her marriage, she becomes an anonymous artist, unburdened by her restrictive family and marriage. Through art, Lucrezia can find the freedom she craved for her life. In other words, art can be a conduit through which people, especially Lucrezia, can express themselves emotionally. It can also be a conduit through which they can express their power. Though Lucrezia comes from an influential family, she wielded much power—until she became an artist. As an anonymous artist, she wielded tremendous energy and could use it in any way she saw fit—including in criticizing her own family.
