And warms and moves this needless frame, (A fever could but do the same) (15-16)
The body's ambivalence about living really comes out here. It calls itself purposeless and compares the experience of being alive to having a fever—not exactly reveling in the day-to-day.
And, wanting where its spite to try, Has made me live to let me die. (17-18)
The body sums up why it hates the soul. With nothing else to torture, the soul decided to use its own body to do its worst: bring it to life. But hey, isn't that better than never existing at all? Not according to the body, it isn't. Its conclusion is that there's no point to living if you're only going to die.
A body that could never rest, Since this ill spirit it possest. (19-20)
One of the worst things about being alive is always being on the move. Take a chill pill already! Remember from stanza one that the soul was venting about being confined and imprisoned: it wanted more movement. Here the body is complaining about exactly the opposite.
And all my care itself employs; That to preserve which me destroys; (25-26)
Here's what realllly bugs the soul: the body's instinct for survival. It uses everything it has—its immune system, its ability to walk to the pharmacy to get medicine, its capacity for hope—to fight off death. This is exactly what the soul does not want. What could be more annoying than watching your sworn enemy use your own skills against you? Hello? I'm the reason you can even feel hope.
Constrain'd not only to endure Diseases, but, what's worse, the cure; (27-28)
Not only does the soul have to suffer through the body's diseases, forced to translate physical symptoms into conscious thoughts like, "Ugh, I want to puke"; it also has to endure being cured, knowing that death would set it free.
And ready oft the port to gain, Am shipwreck'd into health again. (29-30)
The soul's longing for death sets up this perfect paradox at the end of stanza three: just as it's about to bump up against the dock of death, the body sinks it back into life.