Along with Juliet's nurse, Friar Laurence indulges the adolescent whim of Romeo and Juliet to get married. The nurse is somewhat less culpable than the friar in that...
In Shakespeare's' Romeo and Juliet, kind-hearted Friar Laurence is as least partly responsible for the deaths of Romeo and Juliet.
Along with Juliet's nurse, Friar Laurence indulges the adolescent whim of Romeo and Juliet to get married. The nurse is somewhat less culpable than the friar in that she simply encourages Juliet's romantic notions out of her indulgent love for Juliet, but Friar Laurence actually performs the marriage—hastily, in secret, in spite of their feuding parents' wishes, and despite his own better judgment.
FRIAR LAURENCE. So smile the heavens upon this holy act
That after-hours with sorrow chide us not! ...
These violent delights have violent ends
And in their triumph die, like fire and powder,
Which, as they kiss, consume (2.6.1-2, 9-11).
Friar Laurence has an ulterior motive for agreeing to marry Romeo and Juliet. He believes that their marriage will end the bloody feud between their families.
FRIAR LAURENCE. In one respect I'll thy assistant be;
For this alliance may so happy prove
To turn your households’ rancour to pure love (2.3.93-95).
This is a fairly unrealistic premise by which Friar Laurence justifies the marriage and on which he bases Romeo and Juliet's fate.
After the marriage night, Juliet runs to Friar Laurence's cell to tell him that her parents have demanded that she marry Paris, and she finds Paris already there, arranging for their marriage.
When Paris leaves, the distraught Juliet begs Friar Laurence to find some way out of this dilemma, and if no remedy can be found, she threatens to kill herself.
JULIET. Be not so long to speak. I long to die
If what thou speak'st speak not of remedy (4.1.67-68).
Friar Laurence devises a "desperate" scheme whereby Juliet drinks a potion that will make her appear to be dead for forty-two hours. She'll be buried in the Capulet's tomb, and in the meantime, Friar Laurence will send a letter to Romeo in Mantua advising him of the scheme, and telling him to come back to Verona to rescue Juliet.
What could possibly go wrong with this impossible scheme?
Juliet takes the potion too soon. Friar John, to whom Friar Laurence entrusted delivery of the letter to Romeo in Mantua, is quarantined in Verona with a family suspected of having the plague—something which is mentioned nowhere else in the play—and Romeo never learns about the scheme. Balthasar travels to Mantua to tell Romeo that Juliet is dead, and, after taking some time to buy poison from an apothecary whose shop is conveniently located just down the street, Romeo rides back to Verona, determined to kill himself next to Juliet.
As a side note, why did Romeo feel it necessary to buy poison to kill himself? He previously threatened to kill himself with whatever was at hand when he was banished from Verona after he killed Tybalt.
ROMEO. (To Friar Laurence) ...Hadst thou no poison mix'd, no sharp-ground knife,
No sudden mean of death, though ne'er so mean,
But ‘banished’ to kill me— (3.3. 45-47)
Later in the same scene, Romeo draws his own sword and threatens to kill himself.
When he returns to Juliet's tomb, Romeo has both a sword and a dagger. He uses the sword to kill Paris, and Juliet uses his dagger to kill herself.
So why did Romeo feel the need to buy the poison?
In any event, Romeo confronts and kills Paris at Juliet's tomb, enters the tomb, finds Juliet apparently dead, drinks the poison, and dies.
When Friar Laurence learns that Friar John failed to deliver the letter to Romeo explaining his scheme, he rushes to the graveyard. Friar Laurence enters the Capulet's tomb to find the bodies of Romeo and Paris, just as Juliet awakens too soon from the sleeping potion, before Friar Laurence can arrange for her to be taken away from the death scene.
JULIET. O comfortable friar! where is my lord?
I do remember well where I should be,
And there I am. Where is my Romeo? (5.3.153-155)
Friar Laurence hears a noise and panics.
FRIAR LAURENCE. I hear some noise. Lady, come from that nest
Of death, contagion, and unnatural sleep.
A greater power than we can contradict
Hath thwarted our intents. Come, come away.
Thy husband in thy bosom there lies dead;
And Paris too. Come, I'll dispose of thee
Among a sisterhood of holy nuns.
Stay not to question, for the watch is coming.
Come, go, good Juliet. I dare no longer stay.
JULIET. Go, get thee hence, for I will not away (5.3. 156-165).
Friar Laurence knows that Juliet has already threatened suicide if she's forced to marry Paris, and now Romeo lies dead next to her. At the time of Juliet's greatest need, the kindly, good-hearted Friar Laurence turns coward and runs away. Within mere minutes, Juliet kills herself with Romeo's dagger.
With the deaths of Romeo and Juliet, Friar Laurence achieves his dream of ending the feud between the Capulets and the Montagues.
Friar Laurence doesn't achieve his goal of "pure love" between the feuding families, but Romeo and Juliet's deaths reduce the level of contention between the families from outright bloody hostility to intense competition. This is exemplified in the dialogue between Lord Capulet and Lord Montague regarding their monuments to Romeo and Juliet.
CAPULET. O brother Montague, give me thy hand.
This is my daughter's jointure, for no more
Can I demand.
MONTAGUE. But I can give thee more;
For I will raise her statue in pure gold,
That whiles Verona by that name is known,
There shall no figure at such rate be set
As that of true and faithful Juliet.
CAPULET. As rich shall Romeo's by his lady's lie—
Poor sacrifices of our enmity! (5.3.307-316)
It's simply a matter of time before this level of competition escalates to the previous level of bloodshed in the streets.