God as Divine Mother is a huge subject in Hinduism. And, it is poorly understood, especially in the western world. In this little book, Sri Aurobindo describes Divine Mother as One with four personalities: Maheshwari, Mahakali, Mahalakshmi and Mahasaraswati. Then He discusses how She plays Her many roles through them. This book contains a lot of Spiritual truths, many of which are not going to be understandable by mere rationalization.
If you think that religion is just faith, this book is not for you. A little background is also necessary to understand the context of this book. There are a number of ways sages have taught us about God as Divine Mother. Shakta Tantra describes Her as Dasa-Mahavidya. Mystic Shaktas have described Her according to the Vedas, Upanishads and Puranas. I have not seen this discussed in any one book, that means, you'll probably have to study a lot to even get the basic ideas.
Divine Mother as Shakti (avyaakrita paramaa prakriti), as Deities (Brahma-mayi, Ichhaa-mayi, Lilaa-mayi and Kaala-bhayahaarini Mother) or in the body as the Kundalini, are not at all easy to understand, even after a lot of study. In this little book, Sri Aurobindo presents Divine Mother in a somewhat easier way, even though the book itself is not that easy to read. You will have to read it again and again. The more you understand this book, the more you will love it, and appreciate the insights into the meaning of worship.