Complex sentence: The "Devi Bhagavata Purana" says Varahi with other Matrikas is created by the Supreme Mother and the Mother promises the gods that they will fight demons when needed.
Split into simpler sentences: The "Devi Bhagavata Purana" says Varahi, with the other Matrikas, is created by the Supreme Mother. The Mother promises the gods that the Matrikas will fight demons when needed.