The word atman has been used to denote the transcendental Self since the time of the ancient Upanishads. Even the etymology of the word predisposes toward this significance since “a” in this word is a negative particle and “tma” means “darkness.” Therefore “atma” or “atman” means “opposite to darkness,” “shining.” As such it is a key concept of Hindu metaphysics.

Atman is Immortal

Atman is the immortal and immutable aspect of mortal existence, which is the substratum of every object of creation including man. The Self is the essential core of one’s being or what is known in the Christian tradition as the eternal soul. It is one’s very essence. In most spiritual traditions of Hinduism, it is considered to be pure Awareness.

The Self cannot be seen, cannot be perceived, cannot be reached, cannot be grasped since It is the seer, the grasper, the observer, the indweller of all embodied beings, and the doer of everything. In other words, the Self reveals itself only to itself.

No finite act of cognition is involved. It is the supreme revelation. In this way the Self becomes the subject, the object, and the means of the experience. Hence the Shiva Samhita (I.62) states:

“Having abandoned the perception of false states [of consciousness], the renouncer of all volition certainly beholds the Self [the object] in the Self [the subject] by the Self [the means of the revelation].”

The Nature of Atman is Indescribable

Its nature cannot be explained or described adequately, as it is beyond the senses and the mind. It can only be revealed when all the sensory activity ceases to impact the mind and when the mind itself is freed from the movement of thoughts and sense objects and the torment of desires. This mystery unfolds when the mind is still and the heart is opened. One enters into (his) Oneness only wearing the robe of stillness.

The word atman means also in some contexts the ego, which shows another truth: that the ego doesn’t have a separate existence from the Self. It is just a reflection of the Self in the mind-mirror. And the mind with its binary system, needs a first and a second and because of this it enthrones the ego as the king giving it the position of control and ownership, whereas in actual reality it is a mere reflection.

The Katha Upanishad explains the relative status of the two selves in this manner:
“There are two selves, the separate ego and the indivisible Atman. When one rises above I, me, and mine, the Atman reveals Itself as the real Self.”

The Mundaka Upanishad is more explicit and poetic: “Like two birds perched on the same tree, intimate friends, the ego and the self, dwell in the same body. The former eats the sweet and sour fruits of life, while the later looks on with detachment.”

And Bhagavad Gita offers us inspiring thoughts about atman:
8:3 …Principle, eternal nature (of all beings) is Atman…

6:7 He who attained Atman obtains the whole world for he finds refuge in the Divine Consciousness, when (his body) finds itself either in cold or heat, happiness or grief, honor or dishonor.

6:10 A yogi should always try to concentrate his mind on Atman…

6:18 When his purified thoughts, devoid of all material desires, are concentrated on Atman alone, he is said to be in harmony.

5:17 He who perceives himself as consciousness, who identifies himself with Atman, whose faith is wholly on the Supreme, who takes refuge only in Him – that one approaches Liberation being purified by Wisdom.

15:11 Yogis who have the right aspiration come to know not only the soul in themselves, but Atman as well. But those lacking knowledge do not find Atman.

2:58 When – like a tortoise drawing its legs and head within the shell – a (yogi)… withdraws his senses from sense objects, then he attains true knowledge.

13:22. The Watching, Sustaining, All-accepting Supreme Lord, and also the Divine Atman – so called in this body – is the Highest Spirit.

13:29. One who sees that all actions are performed in prakriti alone while the Atman remains out of action – that one truly sees.

13:31 Eternal and not bound by prakriti, the Divine Atman though residing in bodies does not act and is not subject to any influence…

15:32 As omnipresent Emptiness does not blend with anything due to its subtlety, so the Atman present in bodies does not blend with anything.

10:8 I am the source of all; everything emanates from Me. The wise ones who come to understand this worship Me with deep delight in their hearts.

10:9 Those whose thoughts dwell in Me, whose lives are surrendered to Me, who enlighten one another and constantly converse about Me – they are fully satisfied and blissful.

We can conclude by saying that the realization of the transcendental Self is the noblest and worthiest ideal of human existence.