The Kena Upanishad is so named because it asks many fundamental questions that begin with the phrase, “by whom” – or “kena”. By whom willed and directed does the mind alight upon objects of the world? The Kena is one of the most metaphysical of the Upanishads, as it discusses the subtle reality of the indestructible Brahman. In conjunction with Chapter 8 of the Gita, it forms a pillar of the knowledge of the One supreme reality. The Kena addresses both the impersonal and personal aspects of Brahman, so as to engage the needs of all levels of truth-seekers.
Om Namah Shivaya is a three word Mahamantra that is considered to be the supreme invocation to Lord Shiva. The gayatri invocation for Lord Shiva is called Rudra Gayatri. Aum tadpurushAya vidhmahe.
The Atman cannot be cut, burnt, suffer any decay or be dried out. The five forces of nature which are capable of destroying physical elements by their combined actions have no influence on the Atman. That is why it is referred to as nitya or permanent or unchangeable.