From Chhandogya Upanishad

Uddalaka said: 'Fetch a fruit of the big fig tree'

Svetaketu said: 'Here is one, Sir.'

'Break it, what do you see there?'

'These little seeds.'

'Crush one of the little seeds.'

'Yes, Sir, I have done it.'

'What do you see inside?'

'Nothing,' said the son.

'Yet in the subtle substance inside that little seed, which your eye does not even perceive, existed all this big branching Nyagrodha tree. Do you wonder at it? Likewise all that exists, this universe, was in that Sat which thou too art. Believe it, dear child, thou art that.'

'If the Sat is the all-pervading cause of all, why is it not perceived clearly?'

As a lump of salt is dissolved in water and disappears, so is the Sat lost from view in the world but is still immanent in everything in the universe, as the salt is present in every part of the water.

'How are we to gain knowledge of the Sat, which is imperceptible?'

Like unto that of a man, blindfolded and carried away by robbers from his own country is a man's condition. The folds of cloth over his eyes being removed by a friend, he recovers the use of his eyes and slowly finds his way home, step by step, enquiring at each stage. So also, the good teacher instructs the seeker of Truth and helps him to unloose his bonds of desire, and saves him from the robbers. The robbers are his past deeds that brought him to this condition. Recovering his sight as soon as the desires and attachments that blind his vision are removed, he finds his way to the Sat. Thereafter, it is only a matter of waiting for natural death.