सर्वमंगलमांगल्ये शिवे सर्वार्थसाधिके ।
शरण्ये त्र्यम्बके गौरि नारायणि नमोऽस्तुते ।।
Devi fought the demon Mahishasur for nine days, from the first to the ninth day of the Hindu almanac and finally slayed him on the ninth night. Since then, She has come to be known as ‘Mahishasurmardini’, the slayer of Mahishasur.
Whenever tamasik, demoniacal and cruel people become powerful and torment the sattvik and religiously virtuous men in the world, Devi repeatedly incarnates for establishing Dharma. Navratri vrat is of this Deity.