You've probably cottoned on that social ambition and social climbing are Big Ideas here (go check out the "Society and Class Theme" for more). To accompany that, there are multiple instances of characters standing up or kneeling down in a decidedly loaded manner.
The first time you become aware of it is in the scene in which the Duchess is proposing to Antonio. After the Duchess puts her ring on his finger, Antonio kneels down in front of her, whereupon she says to him,
This goodly roof of yours is too low built,
I cannot stand upright in't, nor discourse,
Without I raise it higher. Raise yourself,
Or if you please, my hand help you: so.
[He rises] (1.1.408-412)
See, Antonio's a swell guy and all, but the Duchess can't get with him while he's kneeling in front of her as a commoner.
Solution? She marries him, and as she does so she raises him up, both physically and socially, so they're on more even ground. He can't do it himself, though—it's literally and figuratively the Duchess's hand that does the trick. When Bosola finds out that the Duchess has married Antonio, he refers to Antonio as "this trophy of a man / Raised by that curious engine, your white hand" (3.2.288-89).