Shakti and Shâkta by Arthur Avalon (Sir John Woodroffe),

 To know a thing in its ultimate sense is to be that thing. To know Brahman is, according to Advaita, to be Brahman. One cannot realize Brahman the Pure except by being oneself pure (Shuddhacitta). But to attain and keep this state, as well as progress therein, certain specific means, practices, rituals or disciplines are necessary. The result cannot be got by mere philosophical talk about Brahman. Religion is a practical activity. Just as the body requires exercise, training and gymnastic, so does the mind. This may be of a merely intellectual or spiritual kind.