The renewal of the feud between the Montagues and the Capulets is pivotal to the remaining plot of Shakespeare's Romeo and Juliet. For, it reignites the hatred between these two families, a hatred that is fueled now in the younger generation with Tybalt as he espies Romeo and his friends at the masque held in honor of Juliet. Tybalt is incensed by this appearance:
This, by his voice, should be a Montague.
Fetch me my rapier, boy. What, dares the slave
Come hither, cover'd with an antic face,
To fleer and scorn at our solemnity? (1.5.56-59)
It is, perhaps, this forbidden love that stirs Romeo and Juliet to greater passion. Certainly, they feel the need to circumvent any courtship which would be forbidden them and be immediately married. Also, against his own advice of not acting on "violent delights," Friar Laurence is motivated to bypass Church law of posting bans for six months and perform the marriage in hopes of ending the feud.
Then, because of the renewal of the families' hatred for one another, even the sanguine Benvolio is on edge in Act III, stirring Mercutio's excitable nature. When the choleric Tybalt appears, tempers flare, Romeo becomes involved and tragedy ensues. This sets in motion Juliet's predicament because she cannot tell her parents that she is married to a Montague. With Romeo's banishment, he is unaware of all that transpires and is prevented by other circumstances from further knowledge. Thus, because of the fires of hatred between the families, Romeo believes the worst of everyone and slays Paris at the tomb. The pusillanimous Friar flees the tomb just as Juliet awakens and leaves her to fate. Reflecting upon the tremendous impact of the hatred between the Montagues and the Capulets after the tragic and fated deaths of Romeo and Juliet, the Prince remarks upon the destruction wrought by this enmity:
See what a scourge is laid upon your hate,
That heaven finds means to kill your joys with love!
And I, for winking at you, discords too,
Have lost a brace of kinsmen. All are punish'd. (5.3.303-306)
Without question, the renewal of the feud clearly sets in motion all the action of the tragedy.