Mahatma means a great soul, mahatmyam is it's quality. The great soul of the Mother, one without a second, by it's own glory becomes many souls,many little mothers, matrakas and these emantions of the Mother, after finishing their appointed task converge back into the grat soul of the Mother.The story of all these emanations and their deeds, the glory of the great soul of the Mother is delienated in the text which also incorporates the sublime utterance, mahakavya, of the Devi embodying the Upanishadic Truth Of One without a second, viz: I alone am there in the universe. Who is the second person other than me?'. For this reason the text is known as Devi Mahatmyam or Glory Of The Divine Mother.
For upasakas, persons interested in understanding the full power of the Divine Mother this Book is the best guide.