Romeo and Juliet use witty banter, along with religious metaphors and allusions, to flirt with each other during their first meeting. First, Romeo describes his lips as pilgrims seeking their promised reward--a kiss. Juliet quickly plays along but also plays hard-to-get by answering with, "For saints have hands that pilgrims' hands do touch,/ An palm to palm is holy palmers' kiss" (I.v.102-103). More specifically, when an author writes a line using one part of a subject to represent the whole, this is called synecdoche. For example, Romeo refers to his lips as pilgrims and Juliet refers to herself as a saint who actually kisses with her hands. Romeo uses wit to gain his kiss by saying that his lips which pray for relief and that Juliet, the saint, must grant his lips their desire. In fact, he says, "Then move not while my prayer's effect I take./ Thus from my lips, by thine, my sin is purg'd"(I.v.109-110).
The act of kissing is referred to as sin and Romeo is just fine with that. Juliet says that now she is left with his sin, but forgets all about that when the second kiss motivates her to say that he kisses "by the book" (I.v.114).