The right answers are: It foreshadows what is yet to happen to the main characters in the play and it creates an ominous mood that hints at the conflicts of the play. On the one hand, this prologue reveals that, despite the difficulty and the danger that the love that they feel for each other entails - they are supposed to be enemies and, therefore, they cannot court as lovers normally do - they will find the power, and the time, to meet and show their love. On the other hand, the prologue does create a threatening mood that illustrates the conflicts of the play - it reveals that Romeo is not in love with Rosaline anymore (even though he "groaned" for her), that he has fallen in love with Juliet, whose family happens to be in bad terms with his family, that they cannot meet and court as other lovers do, and that their passion (and passion often equals trouble), however, will mitigate their perilous love (the "extremities") with equally extreme "sweet."