How we cite our quotes: (Act.Scene.Line)
Quote #4
[…] Didst thou ever see a lark
in a cage? Such is the soul in the body: this world is like her
little turf of grass, and the heaven o'er our heads like her
looking-glass, only gives us a miserable knowledge of the
small compass of our prison. (4.2.122-26)
Here's part of Bosola's closing performance to bring down the Duchess. Even though the Duchess is literally Ferdinand's prisoner, Bosola tells her that her real prison is her earthly body. We're all trapped, knowing just enough about the world to be aware of our entrapment. Ferdinand is trying to drive the Duchess crazy—to take her out of her body—but Bosola's trying to show her that the real torture is being confined inside of it.
Quote #5
Of what is't fools make such vain keeping?
Sin their conception, their birth weeping;
Their life, a general mist of error,
Their death, a hideous storm of terror. (4.2.181-84)
By now, you should hear these words and think, "hey, that sounds very Bosola-ish." Why? Because it describes a world that isn't just bad (there are several characters who would be onboard with "sin their conception, their birth weeping"), but is, moreover, randomly bad. Bosola's idea of life as a "general mist of error" is validated by his own experiences. How so? Well, more than any other character, Bosola has a bird's eye view of society's corruption, but despite that knowledge even he can't game the system. When he tries to fight back against that "mist," and save Antonio, he ends up accidentally killing him.
Quote #6
The Cardinal: There is a fortune attends thee.
Bosola: Shall I go sue to Fortune any longer?
'Tis the fool's pilgrimage. (5.2.294-96)
The Cardinal is commissioning Bosola to murder Antonio, promising him a whole lotta dough—a "fortune," to be exact. Bosola, in one of many instances of bleak double meanings of this play, turns "fortune" back on itself. He mocks not only the idea of fortune as reward (he's seen with Ferdinand how far the promise of reward gets him), but also the larger concept of Fortune, or Fate. To Bosola, there doesn't seem to be any coherent guiding force in the universe, and if there is, it's hardly sympathetic to the suits of mortals.