Upanishads: The Secret Doctrine of the Upanishads

This is the secret of all secrets. UPANISHADS.... The word UPANISHAD itself means 'secret doctrine'. Why call it secret if you are going to call it doctrine? If it is a doctrine, it cannot be secret; if it is secret, it cannot be a doctrine. So why call it a secret doctrine? Why use two contradictory words? Mystics have always thought that the moment you use a word without also using its opposite, you divide life.
And life exists in contradictions. The negative and positive of electricity exist in deep communion; the male psyche and the female psyche exist in deep communion. Darkness and light - we may think they are contradictions, opposites, polar opposites, but they exist in deep communion.