Answer :
It reminds the reader of the passage of time! It also reminds you that the events are taking place at night, not during the day.
The moon in shakespeare's " A Midsummer Night's Dream " is not only a luminous passive watcher in the night sky, but it is a powerful force.
It does symbolizes love, lust and dreaming and is seen as a power symbolic force that determines and affects human behaviors and reactions.
In the context of the question it does remain you that he events are only taking place at night and the reader of the passage of time.