What is the purpose and foreshadowing of the Prologue?
During the era in which Romeo and Juliet would have first been performed, very few if any props would have been used and the set was extremely limited. Characters relied on costuming and colorful language to paint the scene for an audience.
Most theater performances during the time of the Globe Theatre contained prologues that told the audience what to look for in the coming minutes and hours.
Today, we can rely on things like music, special effects, and elaborate sets to contribute to the telling of a story. They truly had to depend on just a few of the arts.
The purpose of the Prologue is to sort of set the stage and give us a little bit of background. It is from the Prologue that we find out that the Montagues and the Capulets are having a feud.
The Prologue also tells us quite explicitly what is going to happen. It says that Romeo and Juliet (not by name) are star crossed -- that they have been doomed to a bad fate. It says that it is only with their deaths that the feud will end. So that clearly tells us how the play will end.