So, when, after the death of Romeo and Juliet this same crucial character expresses that, “a greater power than [they] can contradict” has controlled their lives and “thwarted [their] intents,” the reader gets a strong impression that a powerful theme is being conveyed.
Nowhere else does he very clearly attribute certain themes to the play before it has truly begun.
No, Shakespeare used a prologue in Romeo and Juliet for a very specific reason.
This becomes even more apparent when Romeo, in his final lines, expresses that in the long-run, the only thing we can really rely on to occur in our lives is that we will all be taken by the “everlasting rest” and be brought back to dust through death.
Everything else: good fortune, health in life, happiness and success all fades away into nothingness when our final hour arrives.