Brahma Sutras systematizes the philosophy of the Upanishads in 555 aphorisms. In this book the original aphorisms are given in Devanagari followed by word-for-word English rendering, and the interpretation of the sutra according to Shankaracharya. The introduction contains a comparative study of the bhashyas of Shankara, Ramanuja, and Nimbarka.
Those who have succeeded in attaching or detaching their minds at will have succeeded in Pratyahara, which means gathering towards, checking the outgoing powers of the mind, freeing it from the thralldom of the senses. When we can do this, we shall really possess character; then alone we shall have taken a long step towards freedom. Before that, we are mere machines.
-Swami Vivekananda