two families did, passively, like a mirror.

County Paris is important to the play in that he serves as a contrast against Romeo to show us just exactly how young and still young-minded Juliet truly is. Paris represents Juliet's alternative more rational choice. Juliet does not actually have a genuine reason to prefer Romeo over Paris. Paris is equally handsome, possibly even more so, as we see from Lady Capulet's opinion that, "Verona's summer hath not such a flower," and the Nurse's agreement (I.iii.81). Paris is older, wiser, and has the higher noble rank of a Count, showing us that he can provide for her far more fully than Romeo ever could. Not only that, Paris genuinely loves Juliet, as we see from his persistence in asking for her hand and from his genuine grief over her faked death. However, Juliet allowed her young emotions to be swept away by Romeo simply because he was far more forward with her and even gave her her first kiss. Thus, Paris serves to represent adult, rational thought in contrast to Romeo, who represents youthful emotionalism.

Prince Escalus is very important to the play in that he represents the deep, booming voice of justice, law, and even of philosophy. He acts as the voice of law by laying down the harsh penalty of death should the two families battle in the streets of Verona again. He acts as the voice of justice by justly sentencing Romeo to banishment instead of death for killing Tybalt when he learned that Tybalt had started the quarrel and even slayed the prince's own kinsman, Mercutio. He frequently acts as the voice of philosophy by referring to Lord Capulet and Montague as "beasts" for spilling blood to "quench the fire of [their] pernicious rage" (I.i.80). He further acts as the voice of philosophy by showing us just how much damage Capulet's and Montague's feud caused. We see this in his lines in the closing scene,

Capulet, Montage[Montague],
See what a scourge is laid upon your hate,
That heaven finds means to kill your joys with love! (V.iii.301-304)

Without Prince Escalus's wisdom, the readers/viewers would not truly be able to pin hatred as the true cause for all of the death in the play.

Prince Escalus arrives to break up a street brawl and says that the history of the feud is bloodshed. He describes this bloodshed from the street fighting as

purple fountains issuing from your veins

The prince calls the feuding men "beasts" and recounts a history of three recent street fights based on nothing more than "an airy word." In other words, the prince accuses the Capulets and Montagues of fighting for no legitimate reason. He mentions too that the fighting is not only done in part by older men but is an old feud, implicitly as rusty as the weapons the men use to fight with.

Prince Escalus is clearly angry and fed up that the street brawling has erupted three times recently, disturbing the peace of Verona. He tells the feuding families they will have to cut it out. He states that if anyone is caught street fighting again, they will be executed as a result.

This can be found in Act I, Scene 1, when the Prince comes in and sees the aftermath of the fight between the servants.

The Prince just says that the families have been feuding for a long time.  He does not say why they do not like each other.  We never do find that out.  He says that they have fought out in the public streets three times, just because of comments that have been made (this appears to be just in recent times).

The Prince says that anyone fighting in public again will be subject to the death penalty.  His exact words are:

If ever you disturb our streets again,
Your lives shall pay the forfeit of the peace.

After the street fight in the beginning of Romeo and Juliet, Prince Escalus appears with his attendants.  Angered that no one at first hears him, he calls them "Rebellious subjects, enemies to peace" (I,i,54).  Stating that this brawl is the third of those between the Montagues and the Capulets that have disturbed the peace of Verona, the Prince tells the old enemies,

If ever you disturb our streets again,/Your lives shall pay the forfeit of the peace. (I,i,70)

That is, the Montagues and the Capulets cannot fight again or the Prince will have them killed.

Here in this speech of the Prince, the audience witnesses the juxtaposition of images that are in the Prologue; the Prince uses the same word play to make his point to the warring families:  "Rebellious subjects," "men/beasts," "canker'd peace/canker'd hate."

He is the ruler of Verona, and not an effective one, as three brawls between these rival families have broken out on his watch ("Three civil brawls, bred of an airy word"). We can take "airy word" to mean these fights start over nothing, and have escalated quickly. As he finishes admonishing the families for fighting, he warns them "your lives will pay the forfeit" if there is one more brawl. But later, after Romeo kills Tybalt, Escalus banishes him instead of killing him ("We presume to stop the continued family once again").

When he gets what he wants (an end to the fighting), it comes at a great cost. Consider his last words...

A glooming peace this morning with it brings;
The sun, for sorrow, will not show his head:
Go hence, to have more talk of these sad things;
Some shall be pardon'd, and some punished:
For never was a story of more woe
Than this of Juliet and her Romeo.