This potion made it so that the servant told romeo that he saw her dead When Romeo leaves Verona, he becomes desperate to rejoin Juliet. Because he’s out of town, Romeo is also out of the loop from Friar Lawrence’s plan to fake Juliet’s death.
Friar Lawrence explains, “The letter was of dear import,” but it could not be delivered because Romeo is hard to track down outside of Verona (Shakespeare 232). The fake news about Juliet’s death would not have been delivered to Romeo if he had not been banished.