have resonated very closely with the audience that had just been through it themselves.

Friar Laurence’s letter never reached Romeo because its messenger Friar John was stopped by a plague.

When Romeo was banished for killing Tybalt, Friar Laurence tried to be in communication with him so he would not be cut off completely from his new bride, Juliet. One of the most serious problems that occurred right off the bat was Juliet’s forced marriage to Paris.  Juliet went to Friar Laurence for help, and his solution was to fake her death.  This was only a good idea, though, if Romeo was in on the plan. 

Friar Laurence wrote a letter to Romeo explaining what was going on.  Imagine his surprise when he found out that it never reached its destination.  Friar John arrived, and told Friar Laurence the bad news. 

FRIAR JOHN

Going to find a bare-foot brother out
One of our order, to associate me,
Here in this city visiting the sick,
And finding him, the searchers of the town,
Suspecting that we both were in a house
Where the infectious pestilence did reign,
Seal'd up the doors, and would not let us forth;
So that my speed to Mantua there was stay'd. (Act 5, Scene 2)

Friar Laurence asked the obvious question: Who took the letter to Romeo then?  The answer, unfortunately, is no one.  Friar Laurence was upset, and told him that the letter was important.  He feared that Romeo would do something rash, because he knew Romeo. 

Romeo did do something rash.  He got himself a vial of poison, went to Juliet’s tomb, and poisoned himself.  Juliet awoke to find the husband she had gone to so much trouble to stay with dead by her side.  Devastated, she committed suicide with his dagger.  Naturally, Friar Laurence blamed himself. It is another example of circumstances really being against these two.  They pushed fate and lost.  You could say they had really bad luck.

In Act V, Scene 2, Friar John is not able to get to Romeo because there was suspicion of a plague and anyone who was trying to enter Mantua was quarantined.  No one would take Friar Laurence's letter from Friar John because they were afraid they might catch the plague.  Therefore, Romeo never received word that Juliet was in a deep sleep, induced by herbs, and would wake up.

The note from Friar Laurence never reaches Romeo because Friar John, who was to deliver the message, was quarantined in a house because they thought he had been exposed to the plague.

By the time that Friar John is able to relay this information to Friar Laurence, Romeo has already been told by Balthasar that Juliet has died and Romeo has returned to Verona.

Going to find a barefoot brother out,(5)
One of our order, to associate me
Here in this city visiting the sick,
And finding him, the searchers of the town,
Suspecting that we both were in a house
Where the infectious pestilence did reign,(10)
Seal'd up the doors, and would not let us forth,
So that my speed to Mantua there was stay'd.

Friar John had been sent by Friar Lawrence to deliver the letter to Romeo in Mantua.  Before Friar John had left the city of Verona, he had gone to find another Franciscan friar to "associate" with, that is, to accompany him on his journey to Mantua.  At that time, the "searchers", which were a kind of medical-police watch of the town, suspected that there was plague in the house of the other Franciscan friar. So, as a precaution to prevent widespread infection, they sealed up the doors and prevented anyone from leaving the house.  Friar John was thus trapped inside, and unable to leave the city and get to Mantua.

As the reader would surmise, this is event on which the entire plot hinges in this last act.  Since Friar Lawrence had someone else deliver the letter, he lost control over the timing of the delivery.  The letter contained vital information for Romeo: namely that Juliet was not dead, as he would hear shortly, but had taken a potion which would make her appear dead for a period of time.  The knowledge of this would make a huge difference to Romeo; it would prevent him from taking rash actions, such as coming back to Verona (or killing himself.) 

This event is made all the more tragic by the fact that previously unknown characters (Friar John and his friar friend) are the ones at fault for the failure to deliver the letter.  The decision by Friar Lawrence to have Friar John deliver the letter was a fatal one, although made in all innocence.  The fact that the two friars were shut up in a plague-suspected house by city authorities absolves them of any guilt in the matter, for there was no way they could have left and not risked arrest or death.  The guiltless nature of these characters in this affair shows to the audience how elaborate deceptions can so easily go awry.