Durga Saptashati Anushthan- It is said in Bhuvaneshwari Samhita - Just as 'Veda' is eternal, in the same way, 'Saptashati' is also eternal. Just as the best granth of yoga is the Gita, similarly 'Durga Saptashati' is considered to be the best granth of Shakti puja.
In each character, seven goddesses are mentioned in the stotra. Brahmi, Maheshwari, Kaumari, Vaishnavi, Varahi, Narasimhi, and Chamunda (Shiva) Thus the greatness and experiments of 21 goddesses are given in these three characters.
When Maa Durga set out to slay the demons Rakta and Beej, she assumed the form of Mahishasura Mardini. Durga Saptashati is the Brahmastra and Mritsanjivani. It is a ritual to fulfill all wishes, such as no one getting married, trouble in married life, disturbance in the house, money problem, debt, any person in the house is suffering from disease or Pretbadha. Then Navchandi, Shatchandi, or Sahastra Chandi should be recited.