Twelfth Night begins with the sentence “if music be the food of love, play on.” Orsino equates the nature of slow music with love. It sounds lovely until it becomes boring with its excess.

The play also develops in the same way. In the beginning, everything is full of sentiments and slowly the real nature starts becoming obvious to us. Almost all of the Shakespearean comedies deal with the theme of love.

The play evokes the colorfulness of a romantic world. While we learn the feelings of Orsino for Olivia and his persistent appeal to her, we also learn the many layers of such an experience which tells us how foolish sometimes we become in love. 

The love shown in the play is courtly love in nature. Courtly love is a characteristic feature of Elizabethan age. The love triangle between Orsino, Olivia, and Viola, shows us the pretentious beliefs of love.

All of them idealize something but unconsciously want something else. Out of social convention, Orsino worships Olivia. Orsino, Olivia, and Viola, all of them fall in love at first sight.

Orsino says in the first scene that “when mine eyes did see Olivia first, methought she purg’d the air of pestilence; that instant was I turned into a hart, and my desires, like fell and cruel hounds, e’er since pursue me.

Viola at first sight of Duke Orsino without even knowing him says that “myself would be his wife.” Olivia at the first sight of Cesario/Viola/Sebastian says that “even so quickly may one catch the plague?” Such is the approach of the play towards the topic of love.

In a much courtly fashion, the play also shows love as something which makes people melancholy. It is shown as a kind of illness and that’s why throughout the play love is referred to as “plague” or “pestilence” or something similar. It causes pain and makes characters behave irrationally. 

To understand why Orsino and other characters fall in love in such a way, we must know the Elizabethan world view. In such an age, especially courtly people acquired too much knowledge.

They started treating emotion for the sake of treating. This is why the characters in this play seem to have fallen with the idea of love, not truly in love. It is a major thematic concern in this play.