Romeo and Juliet question - help!

I have this question regarding Romeo and Juliet which I need help in:

"Two such opposed kings encamp them still
In man as well as herbs, grace and rude will;
And where the worses is predominant
Full soon the canker death eats up that plant"

(ACT II, Scene 2, 23-26)

Question:

To what extent does this statemtn hold true as far as the unfolding of events in the play goes?

Who is similar to these herbs and how?
Your inputs are dearly appreciated.

Thanks in advance!