In act 1, scene 1, lines 116-121, Theseus tells Hermia:
For you, fair Hermia, look you arm yourself
To fit your fancies to your father's will;
Or else the law of Athens yields you up
(Which by no means we may extenuate)
To death, or to a vow of single life. (I i 116-121)
This is the problem that initiates the action in the play. Hermia will not marry the man whom her father, and thereby the law of Athens, insists that she marry. She refuses to "fit her fancies to her father's will", in other words she resists society's demands and desires to follow her own will instead.
This conflict between the individual and authorities (parents, society, the state) is one of the most basic and most common in all drama.
In the introduction to the Arden edition of the play, Harold Brooks writes that "the theme of the play is love consummated in marriage." (Brooks 1979: liv) Seen in the light of the words above, the marriage can be seen as a social acceptance of individual love.
Hermia and Lysander elope to escape the oppression of a "father's will" and "the law of Athens." But they lose themselves in the forest, and there the fairies manipulate the lovers in more subtle ways than forceful society does. By the play's conclusion, the individuals' desires have been adjusted according to society's needs.