Why do you think Shakespeare chose to indicate the sad conclusion of the play at the beginning of "Romeo and Juliet"?

Shakespeare wants us to know from the start that there is a lesson to be learned in this story and he wants to be sure that the audience "gets it." The theme (and the lesson) is that Revenge creates a no-win situation. The fueding that is continuing between these two families is a source of grief and sadness for both sides. Now, their fueding has caused both families to lose that which they love most. Romeo and Juliet are the future. Without them, there will be no grandchildren and no one to carry on the families' fortunes. So all the fighting was for naught.

This is Shakespeare's best and most timeless play. That is why the story keeps getting told over and over, both as Shakespeare's story and remade into different time periods such as "West Side Story" and "Mississippi Masala."

Shakespeare, like many writers today, despises war and violence and did his small (actually quite big) part in communicating to the world that war and revenge are just not worth the consequences.