In the text of Romeo and Juliet, there are several instances of foreshadowing that Romeo and his love will marry, but that their love would experience difficulties. This foreshadowing prepares readers for the action that follows.
Romeo is absolutely dazzled when he first sees Juliet:
Oh, she doth teach the torches to burn bright!
It seems she hangs upon the cheek of night
Like a rich jewel in an Ethiop's ear--
Beauty too rich for use, for earth too dear! (Act I, Scene 5, lines 42-45)
- Romeo makes certain that he meets Juliet.
Romeo approaches the fair Juliet at the feast and speaks to her. As he does so, Romeo uses the metaphor of a pilgrim wishing to touch the hands of a saint, lending his physical urges some spirituality.
Have not saints lips, and holy palmers, too?...
Oh, then, dear saint, let lips do what hands do (Act I, Scene 5, lines 100-102).
Juliet acquiesces, indicating she is taken with Romeo, too. In Act II, as Juliet daydreams of Romeo and ponders the import of his family name, she wishes that he could change his name, an impossible task.
Romeo overhears her and replies to her, and in his idealism, he declares that he will gladly change his name. Juliet indicates her passion for Romeo, and he responds. Impulsively, they agree to marry, and Romeo rushes off to Friar Laurence. When he meets with the Friar, Romeo declares his love for Juliet and asks the priest to perform the marriage ceremony for them. The friar warns Romeo:
These violent delights have violent ends.
And in their triumph die, like fire and powder
Which as they kiss consume (Act II, Scene 6, lines 9-11).
The priest urges Romeo to "love moderately" and long love will come about. He soon realizes that Romeo will not listen to reason. So, rather than send them away to sin with one another, the friar decides to marry them, hoping that this marriage will ameliorate the hostility between the two families.
All the instances cited propel the action to a dangerous pitch and suggest to the audience that there will be difficulties for Romeo and Juliet in their love for each other.