It is by giving lights that the celestials have become gifted with beauty, energy, and resplendence. By abstention from such a deed, the Rakshasas have become gifted with the opposite attributes. Hence, one should always give lights.
देवास्तेजस्विनो ह्यस्मात् प्रभावन्तः प्रकाशकाः। तामसा राक्षसाश्चैव तस्माद् दीपः प्रदीयते॥