What is the purpose of the festival of diwali? when dose it take place?

The festival of Diwali has a deep history which is connected to the Hindu religion, however anyone can celebrate it including non-Hindu's. In short, it is the celebration of the return of Lord Rama and Goddess Sita along with Lakshmana from 14 years of exile which they had to suffer from even though they did nothing wrong. For more information, I recommend doing some research on the Ramayana or watching/reading it because even if you are not Hindu, you will still gain useful knowledge about life and useful morals from it. I hope this helps :)

silk

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rice

all the other answers are wrong