Act two, scene three, opens with Friar Lawrence gathering herbs and plants in his basket as he muses at the duel properties of the plants he collects. When Friar Lawrence contemplates how the rind of a specific flower can be used as both a powerful medicine or deadly poison, he compares the two opposite elements present in the flower to the dual nature of mankind. Friar Lawrence says,

Two such opposèd kings encamp them still, In man as well as herbs—grace and rude will (Shakespeare, 2.3.28-29).

Friar Lawrence is essentially noting that in both nature and mankind, two opposite elements exist, which are both good and evil. He contends that there is a potential for good in everything and also believes that there is nothing too good that cannot be turned evil if put to the wrong use. Friar Lawrence's comment corresponds to the paradox that exists in Romeo and Juliet's relationship. While their love would typically be perceived as a positive element, the controversial situation surrounding their marriage leads to destruction and death, which can be perceived as "evil" and bad.