How we cite our quotes: (Line)
Quote #4
Joy's cheerful madness does perplex,
Or sorrow's other madness vex; (37-38)
Joy and sorrow are described as twin crazies, one making us so happy it's kinda weird and the other making us so sad it's really annoying.
Quote #5
Which knowledge forces me to know,
And memory will not forego (39-40)
The "which" here is a relative pronoun or stand-in for all the complaints the body's just listed: the madness, the ulcers, the love-pestilence, the cramps, and the shaking. The emotional knowledge provided by the soul forces the body to experience all this stuff, while the memory (also operated by the soul) makes sure the body can't forget it.
Quote #6
What but a soul could have the wit
To build me up for sin so fit? (41-42)
Soul, you better hide yourself. The body's been pretty peeved throughout this stanza, but in the final four lines, the tone becomes quietly devastating, full of these scary accusations. "Who but a soul" heaps contempt on that spiritual powerhouse, implying that only something as tyrannical and malicious as a soul could come up with anything this mean. By teaching the body about emotion and feeling, the soul opened it up to the possibility of sin. And that's a serious bummer.