Though to itself it only live and die; (10)
One of the key points of the nature imagery in this poem seems to be that nature doesn't have a point: it's simply there, existing in and of itself. Could the idea be that the powerful people are like nature because they're good simply by existing? Is this really an appropriate way to think about people? Don't people have responsibilities to one another, as well as to themselves?
But if that flow'r with base infection meet,The basest weed outbraves his dignity. (11-12)
Doesn't it seem like the nature imagery breaks down in these lines? Do flowers really have "dignity"? (Personification alert!) Are weeds really "base"—except in the eyes of human gardeners? If Shakespeare began this quatrain by comparing humans to flowers, it looks like he's ending it by comparing flowers to humans. What effect does this turnaround have on the poem?
Lilies that fester smell far worse than weeds. (13-14)
This final bit of nature imagery shows the same contradictions as Lines 11-12. On the one hand, it's clear that people are being compared to flowers: the "Lilies that fester" are like the powerful people, once they do bad things and hurt people. But this badness is all relative. Nature doesn't care about how lilies or weeds smell (though maybe some animals, who are part of nature, do); it's humans who find the smell of rotting lilies gross. Does this mean that Shakespeare doesn't take the nature imagery entirely seriously—and that the poem is really all about human perceptions after all?