When Romeo and Juliet first meet, the language is poetic and full of depth. This reinforces the idea that the lovers are star-crossed and meant to fall in love.
Before he meets Juliet, Romeo is severely depressed. His girlfriend dumped him, but his friends make him go out. He does not want to go to a party. Yet once there, he sees a girl and instantly finds a few choice metaphors.
O, she doth teach the torches to burn bright!...
Did my heart love till now? Forswear it, sight!
For I ne'er saw true beauty till this night. (Act 1, Scene 5)
Romeo is instantly in love. He forgets about every other girl. He thinks only of this girl he has never met before, whose name he does not know.
When Juliet sees Romeo, she seems to share his feelings. We know because they immediately exchange poetry. Her first words to him are a figurative response to his opening lines, the beginning of a sonnet.
Good pilgrim, you do wrong your hand too much,
Which mannerly devotion shows in this;
For saints have hands that pilgrims’ hands do touch,
And palm to palm is holy palmers’ kiss.(Act 1, Scene 5)
In Shakespeare's day, poetry was the language of love. A young man would write the young lady a sonnet to show he cared. The fact that Romeo and Juliet write poetry together, off the cuff, in the way they talk to each other not only reinforces that they have fallen in love at first sight but also establishes them as star-crossed. They are immediately on the same wavelength, because they were meant to be together.