Two of the main themes, within A Midsummer Night's Dream, are love and magic. Bottom, the object of Titania's love, speaks to the theme of love directly. It is this love which brings about the other theme, magic.
Puck, the prankster of the play, decides to turn Bottom's head into that of an ass. Here is where the other theme comes into play (in regards to Bottom). It is only through Puck's magic that Bottom is able to be transformed.
Therefore, it is through Bottom that readers, or watchers, of the play come into contact with different aspects of love and of magic. The love shown in the play is consequently, only existing for Bottom when he looks like a donkey and Titania is under a spell. Regardless, Bottom is a character whose being is entwined with the themes of love and magic in the play.