"the nucleus of all things, Atman, Life, the Divine, the Absolute"

The Upanishads as translated by Eknath Easwaran explain the concept of the Atman as a part of the Supreme Being: “As long as we think we are the ego, we feel attached and fall into sorrow. But realize that you are the Self, the Lord of life and you will be freed from sorrow. When you realize that you are the Self, supreme source of light, supreme source of love, you transcend the duality of life and enter the unitive state.”

The Mundaka Upanishad, explains this theme with a metaphor in which Brahman is seen into two forms. “Like two golden birds perched on the self same tree, intimate friends, the ego and the Self dwell in the same body. The former eats the sweet and sour fruits of the tree of life while the latter looks on in detachment.”

In the metaphor,  the bird that eats the fruit is the Individual Self, while the bird that is detached is the Universal Self or Divine Force.