The self-existent Lord pierced the senses to turn outward. Thus we look to the world outside and see not the Self within us. A sage withdrew his senses from the world of change and, seeking immortality, looked within and beheld the deathless self. – Katha Upanishad
As pure water poured into pure water becomes the very same, so does the Self of the illumined man or woman verily become one with the Godhead. – Katha Upanishad