Friar John tells Friar Laurence that Romeo did not get the letter about Juliet.
After Romeo was banished, Friar Laurence developed a complicated plan to keep Juliet from having to marry Paris. It involved Juliet taking a potion that would make her look dead, resulting in her burial in the Capulet tomb. The idea was that Romeo would be warned about this by letter. Unfortunately, the letter was waylaid by a plague. Friar Laurence finds out the letter did not get where it was intended when Friar John tells him about the plague.
Who bare my letter, then, to Romeo?
I could not send it,—here it is again,—
Nor get a messenger to bring it thee,
So fearful were they of infection (Act V, Scene 2).
The plague is very serious. Still, Friar Laurence is not happy that Romeo did not get his letter. He says the letter was of “dear import.” Laurence tells John to get a crowbar and meet him. John agrees, and they part.
By the time Laurence gets to Juliet’s tomb, it is too late. Romeo already killed Paris and saw Juliet. He assumes she is dead and kills himself with poison he brought with him. Juliet wakes up a little too late, sees Romeo is dead, and kills herself with his dagger.
Naturally, Friar Laurence blames himself for all of this. He explained to the Prince, Montague, and Capulet how Romeo ended up dead next to Juliet, who appeared to have died a second time. Friar Laurence everyone the whole story, including the part about the letter.
. . . I writ to Romeo,
That he should hither come as this dire night,
To help to take her from her borrow'd grave,
Being the time the potion's force should cease.
But he which bore my letter, Friar John,
Was stay'd by accident, and yesternight
Return'd my letter back (Act V, Scene 3).
Since he had good intentions, Friar Laurence is pardoned. He was glad that, despite the death of so many young people, the events brought an end to the feud. That was his goal, and at least he accomplished it.