My only love sprung from my only hate! Too early seen unknown, & known too late! Prodigious birth of love it is to me, that I must love a loathed."
Juliet says this when she finds out who Romeo is. She's expressing a bunch of information and emotion all at once here—she's fallen in love with Romeo, but she's upset that he is a Montague. She saw him first (too early) and fell for him before she found out who he was (a Montague). Love now seems very strange to her, that she can love someone she's supposed to hate.