Reductively, the theme of Twelfth Night is the joy and pain of love. The play was written in Shakespeare's older years and he attempts to see love for all that is both good and bad about it. This may explain why Twelfth Night has a subtitle, What You Will (the only play that has one, btw). What you want to take away from it, where you are in your life, or how love has treated you over the years will affect your interpretation.
As for the characters who experience the pain of love: there is Malvolio, who falls so madly in love with Olivia that he loses all sense of reality and is eventually becomes a lunatic, having to be physically restrained. Or Orsinio, who falls so in love he likens it not to ectsasy but to disease.
A comedy first and foremost, everything turns out happily in the end and the more tender elements of love are revealed. The whole Cesario/Viola thing has been straightened out, the Duke marries Viola, etc. But throughout the merriment, there are sharp rocks just beneath the seemingly gentle waters of comedy, ready to bruise the feet of anyone who steps into its current unaware.
Love as a Cause of Suffering
Twelfth Night is a romantic comedy, and romantic love is the play’s main focus. Despite the fact that the play offers a happy ending, in which the various lovers find one another and achieve wedded bliss, Shakespeare shows that love can cause pain. Many of the characters seem to view love as a kind of curse, a feeling that attacks its victims suddenly and disruptively. Various characters claim to suffer painfully from being in love, or, rather, from the pangs of unrequited love.
Love is also exclusionary: some people achieve romantic happiness, while others do not. At the end of the play, as the happy lovers rejoice, both Malvolio and Antonio are prevented from having the objects of their desire. Malvolio, who has pursued Olivia, must ultimately face the realization that he is a fool, socially unworthy of his noble mistress. Antonio is in a more difficult situation, as social norms do not allow for the gratification of his apparently sexual attraction to Sebastian. Love, thus, cannot conquer all obstacles, and those whose desires go unfulfilled remain no less in love but feel the sting of its absence all the more severely.
The Uncertainty of Gender
Gender is one of the most obvious and much-discussed topics in the play.Twelfth Night is one of Shakespeare’s so-called transvestite comedies, in which a female character—in this case, Viola—disguises herself as a man. This situation creates a sexual mess: Viola falls in love with Orsino but cannot tell him, because he thinks she is a man, while Olivia, the object of Orsino’s affection, falls for Viola in her guise as Cesario. There is a clear homoerotic subtext here: Olivia is in love with a woman, even if she thinks he is a man, and Orsino often remarks on Cesario’s beauty, suggesting that he is attracted to Viola even before her male disguise is removed. This latent homoeroticism finds an explicit echo in the minor character of Antonio, who is clearly in love with his male friend, Sebastian. But Antonio’s desires cannot be satisfied, while Orsino and Olivia both find tidy heterosexual gratification once the sexual ambiguities and deceptions are straightened out.
The Folly of Ambition
The problem of social ambition works itself out largely through the character of Malvolio, the steward, who seems to be a competent servant, if prudish and dour, but proves to be, in fact, a supreme egotist, with tremendous ambitions to rise out of his social class. Maria plays on these ambitions when she forges a letter from Olivia that makes Malvolio believe that Olivia is in love with him and wishes to marry him. Sir Toby and the others find this fantasy hysterically funny, of course—not only because of Malvolio’s unattractive personality but also because Malvolio is not of noble blood. In the class system of Shakespeare’s time, a noblewoman would generally not sully her reputation by marrying a man of lower social status.
Loving oneself and loving others-the play presents different kinds of love, some of which are less admirable and attractive than others.
Illusion and reality- The play explores the difference between appearance and reality both in a visibly physical sense and on a more profound psychological level. Eg, Madness and dream. Deception and disguise. Self delusion and self-knowledge.
Prig and the prodigal- The play presents us with two extreme ways of life that are equally objectionable in different ways. Whilst Sir Toby's carousing is so profligate and incessant as to be dissolute and debauched, Malvolio's priggish, narrow-minded, self righteousness is so pompous and extreme as to be life denying.