While Diwali is popularly known as the "festival of lights", the most significant spiritual meaning is "the awareness of the inner light".
Central to Hindu philosophy is the assertion that there is something beyond the physical body and mind which is pure, infinite, and eternal, called the Atman. Just as we celebrate the birth of our physical being, Diwali is the celebration of this inner light, in particular the knowing of which outshines all darkness (removes all obstacles and dispels all ignorance), awakening the individual to one's true nature, not as the body, but as the unchanging, infinite, immanent and transcendent reality. With the realization of the Atman comes universal compassion, love, and the awareness of the oneness of all things (higher knowledge). This brings Ananda (inner joy or peace).
The gunas are the underlying forces or tendencies which one needs to have unaffected, direct relation with in order to find effectiveness and righteousness in life: they are lines of potential and illuminate thought and action, thus the inner meaning of Diwali being the festival of lights.
Diwali celebrates this through festive fireworks, lights, flowers, sharing of sweets, and worship. While the story behind Diwali varies from region to region, the essence is the same - to rejoice in the inner light (Atman) or the underlying reality of all things (Brahman).
Diwali or Deepavali is a significant festival in Hinduism, Buddhism, Sikhism, and Jainism, and an official holiday in India.
Deepavali is a Sanskrit word - Deepa meaning light and Avali, meaning a row. It means a row of lights and indeed illumination forms its main attraction. It symbolizes that age-old culture of India which teaches us to vanquish ignorance that subdues humanity and to drive away darkness that engulfs the light of knowledge. Deepavali, the festival of lights even to-day in this modern world, projects the rich and glorious past and teaches us to uphold the true values of life.
Happy Diwali to all of you and your families!