Within the infant rind of this weak flower
Poison hath residence and medicine power. (II.iii.)

Friar Laurence is introduced as he tends to his medicinal herbs. He will later draw on his knowledge of herbs to help Juliet escape her marriage to Paris. One of the central themes of Romeo and Juliet is the inseparability of good and evil, and here the Friar explains that poison and medicine can be extracted from the same plant. The mention of poison foreshadows Romeo’s death.

For this alliance may so happy prove,
To turn your households’ rancor to pure love. (II.iv)

Friar Laurence agrees to marry Romeo and Juliet, and these lines explain his motive. He hopes that the lovers’ marriage will put an end to the feud between their families. However, these lines also serve to remind the audience that according to the Prologue it is not the lovers’ “alliance” but their deaths that will “end their parents’ strife.”

For by your leaves, you shall not stay alone,
Til Holy Church incorporate two in one. (II.vi)

With these lines, the Friar leads Romeo and Juliet to their marriage ceremony. Romeo and Juliet frequently emphasizes pairs coming together to function as one: sex and violence, poison and cure. The play’s central pairing, of course, is the pairing of the two lovers. These lines explicitly remind us that by marrying, Romeo and Juliet become one in the eyes of God and the law.