Romeo has to know that Juliet, although she is thought to be dead, is actually still alive and will wake up and Romeo should be there to meet her.
Of course the letter says that she will wake up Friday night instead of Thursday but at least Romeo would have known she wasn't dead.
Friar Lawrence entrusts Friar John with the important letter to Romeo, instructing him to deliver it to Romeo in Mantua. However, Friar John is unable to get the letter to Romeo in time due to being quarantined.
Friar John
================================================================================================================================================================ ANSWER: In Verona, Friar John tells Friar Lawrence that he was unable to deliver his letter to Romeo due to an outbreak of an infection. =================================================================================================================================================================
Well, that is a complicated question, because no letter like that is delivered: There was a letter to Romeo talking about the false-death plan, but it was never delivered. Friar Lawrence wrote that letter and Friar John was supposed to deliver it, but was unable to due to a quarantine. Balthasar is the one who tells Romeo that Juliet has died (although she has not... this is the false-death that she will awake from), but he just tells him; he doesn't deliver a letter.
Friar Lawrence sends a letter to Romeo, who is in Mantua, detailing his plan to fake the death of Juliet, and have Romeo bring her to Mantua where they can both live happily ever after. He gives the letter to Friar John, who is supposed to bring the letter to Romeo ASAP. Friar John never makes it to Romeo, because he was quarantined due to an outbreak of the Plague. Therefore, he brought the letter back to Friar Lawrence. This messed up Friar Lawrence' plan, as he had already set it in motion.
Romeo and Friar John are not related. Friar John is a Franciscan friar who was supposed to deliver an important letter from Friar Laurence to Romeo, but he was unable to do so due to being quarantined during a plague outbreak.
Friar Lawrence scolds Friar John for not delivering the letter to Romeo informing him about Juliet's fake death. He emphasizes the urgency of the matter and conveys the potential consequences of the message not reaching Romeo on time.
Friar Laurence asks Friar John to deliver a letter to Romeo explaining the plan to fake Juliet's death.
Friar John, who was carrying the message, got himself quarantined.
Friar Lawrence married Romeo and Juliet in his cell.
The plan is that his brother Friar, Friar John, will take a letter to Romeo. But Friar John is prevented from giving him the message.
Quarantine.