The context of Twelfth Night
"One of the many festivals that used to brighten the dark winter months. Christian holidays and the veneration of saints were opportunities in bygone generations for raucous get-togethers, accompanied by overindulgence in food and drink."
Twelfth Night occurred on the twelfth day of Christmas, ie in the dark winter in the northern hemisphere.
This link http://www.novareinna.com/festive/twelfth.html explains it was also known as the "Feast of Fools".
Can you see how the traditions come out in the play Shakespeare wrote? Please explain.