In India almost every  household has a custom of lighting a deepam or diya twice a day â in the morning and evening. This is a part of prayer. All ceremonies daily worship rituals auspicious functions religious occasions as well as  new ventures start with lightning of the lamp. Diya is essential in Hinduism because it signifies purity goodness good luck and power. The presence of light means the non-existence of darkness and evil forces. Since Diwali is celebrated on the new moon day when there is supreme darkness everywhere; people light millions of lamps to get rid of the darkness. It is believed that evil spirits and forces gain power and become active when there is no light. So diyas are lit in every corner of the house to weaken those evil forces. here is a deeper significance to the diya.  The oil in the diya symbolises the dirt in the human mind â such as greed jealousy hatred lust etc â which human beings tend to nurture. The cotton in the diya is symbolic of the atma or the self or the soul. The diya presents light when the oil is burnt by the wick. Hence lighting of the diyas signifies that one needs to get rid of the selfish and materialistic thoughts. This frees one from all forms of sadness guiding the path to enlightenment and to connect with the Supreme Being. Hindu philosophy or belief further states that after the realisation of Atma one must learn to love and serve others unconditionally without any expectations of rewards in return. Such selfless service would bring contentment aanand or happiness in our lives. The external materialistic rewards are only illusions. Hence as a part of purification on Diwali one must endeavour to make one's atma purer. Instead of trying and expecting to change the  world outside change inside.