What is the purpose of the "opposites" theme?

A Midsummer Night’s Dream is built around the concept of opposites or duality. Most every character has an opposite. Consider:

-Bottom is the victim of pranks/Puck plays pranks

-Helena is tall and Hermia is short

-Beautiful Titania (under a spell) falls in love with hideous Bottom

Even groups of characters clash. For example, the craftsmen seem clumsy while the fairies are magical. This all adds to the plays magical atmosphere where everything is not what it seems.