To understand it further, the roots of the Diwali are laid down from Navratri, where, power is asked from Goddess Amba, to fight the evil; both internal and external. Diwali is a day for worship of books of accounts for Vaishyas; this is the time to know the balance throughout the year. Person must make a total of his pluses and minuses throughout the year regarding raag-dwesha, irshaa-matsar etc. This is the day to forget all evil and evil happenings in the past, and to start a pure and loving new year.
Diwali is a festival of candles. The physical candles are a symbol to the internal enlightenment in the inner soul. The external candles make no sense if there is no inner enlightment. Besides, candle gives brightness and removes darkness; similarly our life must be enlightened with God's work eternally.