The primary literary “task” here is “exposition” – telling the audience what has happened in the forest before the play opens, before the development.  Puck is explaining the tensions we should expect in the forest when Oberon and Titania meet, and telling us the cause of the dispute, indirectly giving us hints of the King’s and the Queen’s temperaments, and the relation between them.  Secondarily, the scene sets the stage for the forest mise-en-scene--an imaginary, fanciful place, where fairies hide within acorn cups, etc., not a real English forest.  This is an important contrast to the real world of Theseus and Hippolyta (who are far from quarreling with each other) that brackets the fairy world, and of course a contrast to the real world of the rustics who have crossed over temporarily from one world to the next.  Finally the scene allows us to understand Puck’s role as messenger-peacemaker in the forest, and his role as exposition-narrator to the audience.