The Mother is a brief but important devotional and metaphysical essay written by Sri Aurobindo in 1927 on the divine mother, whome he identified with his spiirtual co-worker Mirra Richard (later known as The Mother).
Later a number of his letters to sadhaks on the subject of the Mother were added, and translations of some of Mirra's Prayers and Meditations. In 1972 all this material was published together as volume 25 of the Sri Aurobindo Birth Centenary Library. This book contains Sri Aurobindo's writing "The Mother" plus his answers on numerous aspects of the Mother's work and powers, and related material.
The whole text is easy to read, the short essay "The Mother" is very inspiring - goes through the four forms or archetypes of the Cosmic Mother (Mahashakti), describing each one in detail. The rest is extracts from letters and what not. Sri Aurobindo's cosmology and soteriology very much revolved around the figure of and worship of the Great Mother, who he saw personified in Mirra