The first recordings of the notion of atman are found in the Upanishads and it isn’t really featured that much in the Vedas.
In the Upanishads, the main teaching is that of Atman-Brahman synthesis. “Though it fills the whole of space, by mysterious way which defies logic, it is proved by experience it dwells in the core of the human heart” [Chandogya Upanishad]
Evidence that supports this is the following passages: “Deep hidden in the heart of every creature” and “as water pure into pure water poured.” Both of this are found in the Katha Upanishad and they show the concept of Atman-Brahman synthesis.
The Upanishads all teach that we all have atman inside us, and that in order to release the atman; the knowledge required (the process of jnana mega) is hard, “Like pith extracted from a reed” [Katha Upanishad] and that it is identical to Brahman, it is Brahman. It is that which lives on
What does the Gita teach about the atman?
The Bhagavad Gita teaches pretty much the same as that which is found in the Upanishads. The authors had to use the same concepts as those found in the Upanishads because the Upanishads are divinely revealed. The teachings are core teachings and so to disagree with them would be to disagree with God.
The gita also teaches that atman is in everyone, and that atman is immortal. The following passage found within the Gita supports this;“who thinks that he can be a slayer? Who thinks that he can be slain?” and “he slays not… is not slain”
This gita encompasses the following quotations to describe the atman “uncuttable, unburnable, unwettable, undryable” In this, the gita tries and succeeds in showing that the atman is not a physical entity, and so the atman is not affected by the material world surround it.
Krishna gives Arjuna an analogy about atman within the Gita, which is that “as a man casts off his worn out clothes and takes on others new; so does the embodied soul cast off his worn out body and enter others new.”
Jamison uses a bit of a more modern analogy of a worn out car. Within his book concerning Hinduism, Jamison writes that “The atman is the driver of a car. When your car wears our, you get out… you are not part of the car.” This is a good analogy of the atman, as it is easy to understand yet still clearly shows that the atman and body are together, but separate.
In his scholarly writings, Bowen says that “the atman is clothed with, though not limited by the psychological components of the individual personality.”
The author of the Gita makes a very big deal that the outward physical body is very different to the inmost self and when a person dies, this marks the end of the physical body but not the atman.
The atman is a key idea within Hinduism, and it is essential in order for us to gain a good understanding about Hindu ethics. Without atman, the concept of samsara, the wheel of transmigration and the ultimate aim of Moksha, Hinduism wouldn’t make sense. The concepts of Moksha and samsara would be scientifically inexplicable and would therefore ultimately fail if the concept of atman were not accepted. Because of this, atman is vital to the religion. Hinduism would not be able to support itself as a religion without this concept, and therefore it’s essential that we understand just how important the concept of atman is to Hinduism.