Twelfth night resounds with songs of the most haunting kind.Discuss how the songs unite the main theme and the sub-theme?

Music in Twelfth Night personify the mood of the characters. In act one, the Duke uses music to soothe his woe over Olivia's constant rejection of him, 

If music be the food of love, play on, Give me excess of it that, surfeiting, The appetite may sicken and so die.

Feste, the clown, also sings about love and lovesickness, 

O mistress mine, where are you roaming? O stay and hear, your true love’s coming, That can sing both high and low.

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