The Prologue is a sonnet — fourteen lines of iambic pentameter with a specific rhyme scheme (ABAB CDCD EFEF GG) — establishing the play's key themes before any action begins. This is Shakespeare's way of setting the audience's expectations: this is a tragedy, and we know from the start that the lovers will die.
The phrase "star-crossed lovers" introduces the theme of fate — the idea that Romeo and Juliet's destiny is written in the stars and cannot be avoided. The word "fatal" carries a double meaning: both "destined by fate" and "deadly."
The oxymoron of "civil blood makes civil hands unclean" highlights the central paradox: civilized people committing uncivilized acts. The feud poisons everything it touches.
Dramatic irony permeates the entire play from this moment — the audience knows the ending before it begins. Every hopeful moment will be shadowed by our knowledge of the inevitable tragedy.
The Prologue also functions as a contract with the audience: Shakespeare promises the play will last "two hours" and asks for "patient ears," a convention of Elizabethan theater.
