Friar Lawrence urges the Capulets to get Juliet to the church quickly because he knows that she is not actually dead.
When she is laid out at the church, or in the mausoleum where she will be ''buried", Friar Lawrence can keep and eye on her. If something were to happen with the sleeping potion that caused Juliet to wake early, she couldn't be seen by the Capulets since they don't know she isn't actullay dead.
