Shankara's doctrine of salvation or liberation (moksha) is defined exclusively in terms of knowledge (vidya) and its opposite, ignorance (avidya). Commenting on Krishna's words in the Bhagavad Gita (13.2), 'The knowledge of the Field [that is to say, the empirical world] and the Knower of the Field is considered by Me to be the knowledge', Shankara quotes a verse from the Katha Upanishad (1.2.4) which might be regarded as the keynote of his teaching: 'Wide apart and leading in different directions are these two, ignorance (avidya) and that which is known as knowledge'.

We find a number of references to being 'firmly grounded in knowledge' (jnana-nishtha) in Shankara's commentary on the Bhagavad Gita, but the knowledge in question is conceived not simply as intellectual and theoretical knowledge but as something existential, amounting to a fundamental change in our outlook and inner nature.