The Mother is whatever is. The essence of pure existence is the Supreme Being or Para Brahman. Mother is whatever is that we know. That which is beyond our knowledge, that is the Purusha, the Supreme Being, the transcendental Para Brahman. That which we know through our mind and senses is nothing but the manifestation of Mother.
She is not only the Universe which we know, this little world and the countless stars, the sun and moon—all these the terrestrial and the stellar, the lunar and the solar systems that comprise this little universe; all this is but an infinitesimal speck in the vastness and infinity that Mother is.
Innumerable such universes have their rise and fall within Her infinite nature. She is all-power and also the great transcendental power at the back of all manifestation, the primal cause for all manifestation and embodiment. She is the very creatrix not only of this world but even the creator, preserver and dissolver of the world. Brahma, Vishnu and Maheshwara have their being in the Mother. She is the Mother of all, countless Brahmas, Vishnus and Maheshwaras.
In as much as She is all-power, all powers are Her play; and therefore all the three dynamic manifestations Brahma, Vishnu and Maheshwara also are modifications of Mother as Adi-Shakti. She is also Brahma-Shakti manifest to us in and through the form of Saraswati, Vishnu-Shakti manifest in and through the form of Lakshmi, and also Siva-Shakti manifest in and through the form of Parvati.