Lord Krishna said: The Imperishable is called the supreme Brahman. Its own sensitive, vibrant expression is adhyātma. Karma is the creative energy unleashing the elements (visargah) with their respective properties.
Brahman is the Imperishable, the source and substratum of all existence and expression. Brahman alone has become the Universe of infinite variety.
When Brahman manifests its sensitivity and vibrancy, generating feelings, awareness and allied factors, it is called adhyātma, the spiritual presence called the Self.
This happens only when apart from the inert pañca-bhūtas, sentience manifests and gives rise to reaction to external stimuli, growth and the like. Creation then becomes two-fold – mobile and immobile.
Among the mobile, human has the best experiential and knowledge potential. He alone can probe into the inner, subject domain, and gain fulfilment!