2 Quotes by Katha Upanishad

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.

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.