What do 9 nights of Navratri stand for?

As per the Kalpas (Puranas), there are three dimensions of Shakti (the feminine energy): Mahakali (strength or power), Mahalakshmi (wealth, passion and material well-being), and Mahasaraswati (knowledge, dissolution, transcendence of the limitations of the mortal body). They are believed to represent the cosmos as the Earth, the Sun and the Moon.

They are also symbolic of the 3 gunas (virtues/qualities): tamas

 (inertia), rajas (activity, passion) and sattva (knowledge, purity), respectively. Therefore, the first three days are dedicated to Durga or Kali, the next three to Lakshmi, and the last three to Saraswati. The tenth day is called Vijayadashmi (or Dussehra) where ‘Vijaya’ means victory – of good over evil, the victory of Lord Rama over the ten-headed demon king, Ravana.