Some of the literary devices that Shakespeare uses in this passage would be:
Simile: <em>"as swift in motion as a ball"</em>
This is used in order to convey an image of very swift, quick movement. This conveys the idea of desperation, as Juliet cannot wait for the nurse to return.
Allusion: "<em>And therefore hath the wind-swift Cupid wings."</em>
In these line, Shakespeare makes an allusion to Cupid, a creature from Greek mythology, often associated with love. This highlights the feelings of love that Juliet is experiencing.
Metaphor: <em>"Therefore do nimble-pinion'd doves draw love,"</em>
In this line, Juliet compares the nurse (who is acting as a messenger), and all other messenger that carry a message of love with doves, as they are also known to carry messages.