According to Vedic sciences, matter reverts to its original form to recreate itself again and again. The creation is cyclical, not linear; everything is recycled by nature - a continuous process of rejuvenation. The human mind, however, lags behind in this routine cycle of creation. Navratri is a festival for one to take the mind back to its Source.
The Mother Divine is recognized not just as the brilliance of intellect (buddhi), but also the confusion (bhranti); she is not just abundance (lakshmi), she is also hunger (shudha) and thirst (trishna). Realizing this aspect of the Mother Divine in the entire creation, leads one to a deep state of Samadhi. This gives an answer to the age-old theological struggle of the Occident. Through wisdom, devotion and nishkama karma, one can attain advaita siddhi or perfection in the non-dual consciousness.
Kali is the most horrific manifestation of Nature. Nature symbolizes beauty, yet it has a horrific form. Acknowledging the duality brings a total acceptance in the mind and puts the mind at ease.
Though Navratri is celebrated as the victory of good over evil, the actual fight is not between good and evil. From the Vedantic point of view, the victory is of the absolute reality over the apparent duality. In the words of Ashtavakra, it is the poor wave which tries to keep its identity separate from the ocean, but to no avail.
The three primordial gunas are considered as the feminine force of our magnificent universe. By worshiping the Mother Divine during Navratri, we harmonize the three gunas and elevate sattva in the atmosphere.