As the only character in Shakespeare's Twelfth Night who remains detached from the play's conflicts, Feste is able to comment objectively upon the foibles and actions of the other characters. For example, in Act I, he comments on Olivia's foolishness in her mourning her dead brother when his soul lies in heaven:
The more fool, madonna, to mourn for your brother's/soul being in heaven. Take away the fool, gentlemen. (I,v,64-65)
In Act II, he supplicates the god of melancholy to protect Orsino because his love-sickness is pure indulgence:
Now the melancholy god protect thee; and the tailor/make thy doublet of changeable taffeta for thy mind/ is a very opal. I would have men of such constancy put/ to sea, that their business might be everything, and their/ intent everywhere; for that's it that always makes a good/ voyage of nothing. Farewell. (II,iv,78-83)
Acting as a foil to Sir Toby, the Puritan, Feste as the "wise fool,"--to use Olivia's term--shows by contrast the bafoonery of Sir Toby, a geste that great entertained the Elizabethans in its ridicule of the reviled Puritanism.
Feste proves to the audience: "Better a witty fool, than a foolish wit" (I,v, 31)
Feste in Shakespeare's Twefth Night is the clown and his role, as with most of Shakespeare's clowns (King Lear, As You Like It) is choric and it works from within the plot of the play. The socially repressed under-class of the clowns are invested with all the driving force in terms of observation, cunning and choric commentary in Shakespeare's comedies and this play is no exception.
1. Feste, as the name suggests shapes the festive and carnivalesque nature of the play. His is a major thematic slant as opposed to Malvolio's melancholy.
2. Feste is a major interconnector between the two plots of the play. He is one of the masters of the gulling of Malvolio plot and with his royal dealings, he has a major role in the main-plot too.
3. His songs are all major thematic evocations and they give the play its structure too. For example, the last song "hey ho the wind and the rain" marks off the festive spirit, bids good-bye to the audience in a self-reflexive way and harps on the idea of an indifferent circularity that characterizes the way of life in Illyria.
4. Feste's character has a strong thematic function. He evokes the most important themes in the play e.g. his analogy between language and the kid-leather-glove, underscoring the appearance-reality theme.