The central theme of Romeo and Juliet is the love that is born in the midst of a feud between families, and what that feud does to it. Around this, the play works with haste, violence, the authority of parents, and chance.
Love and hatred appear stuck together from the beginning. In scene 1 of Act I, Romeo looks at the brawl that has just ended and responds with paradoxes: "O brawling love, O loving hate!" In scene 5, Juliet discovers that the young man she has just kissed is a Montague and says: "My only love sprung from my only hate!" The Prologue already warns that the death of the children will put an end to the discord of the parents.
The love of the two is also haste. In the garden (Act II, scene 2), Juliet compares the night's pact to lightning that vanishes before anyone says "it lightens," and Friar Laurence warns Romeo that "those who run fast stumble" (scene 3) and that "these violent delights have violent ends" (scene 6). They meet at night, at the ball, and marry on the afternoon of the next day.
Violence and family weigh on this love: Mercutio and Tybalt die in the brawl of Act III, scene 1, Capulet threatens to disinherit the daughter who refuses Paris (Act III, scene 5), and peace comes only over the bodies of the children (Act V, scene 3). The play also speaks of fate, with the lovers "star-crossed" in the Prologue and Romeo defying the stars in Act V, scene 1.