The Aparabrahman (which is next to the highest Brahman) that is so minute and subtle is called Jīvātman. Parabrahman is God almighty. It is mentioned in Taittirīyopaniṣad about this aparabrahman as follows : “Tasmād vā etasmādātmana ākāśaḥ sambhūtaḥ, ākāśād vāyuḥ vāyoragniḥ, agnerāpaḥ adbhyaḥ pṛthvī pṛthivyā oṣadhayaḥ oṣadhibhyo annam annāt puruṣaḥ sa vā eṣa puruṣo annamayaḥ.” ‘From this Ātman came into existence ether possessing the quality of sound. From ether air, possessing the qualities of sound and touch, came into existence. Fire with the qualities of sound, touch and colour came into being from air. From fire, water having the qualities of sound touch, colour and taste came into being. From water earth with the qualities of sound, touch, colour, taste and smell came into existence. Vegetation grew from earth, and from vegetation food, from food semen, and from semen Puruṣa came into existence. The materialized form of aparabrahman is the body. Its subtle form is the soul. Jīvātmā or the individual soul is the subtle form of soul dwelling in the materialized form of the aparabrahman. This soul sits in the miniature lotus of heart in the miniature either. The body which is made of the five elements is the dwelling place of this Jīvātmā. The individual life exists in every living being. The body originated from food is the outer covering of the Jīvātmā. This materialized body is also called Annamayakośa (the cask of food). Inside this annamayakośa there is the Prāṇamayakośa (the chest of the life breaths). It is stated in the [Taittirīyopaniṣad] that this Prāṇamayakośa is separate from and existing inside the annamayakośa. The Prāṇamayakośa which exists inside the annamayakośa has the shape of man. The life breath which appears as the inhaling and exhaling breath is the head of the Prāṇamayakośa. The life breath Vyāna is the right wing and Apāna is the left wing, ether its soul and Pṛthvi (the earth) its tail. Inside the Prāṇamayakośa, there exists the Manomayakośa (the chest of mind), but it fills the entire interior of the Prāṇamayakośa. The Vijñānamayakośa (the chest of knowledge or understanding) exists inside the Manomayakośa. The Jīvātmā or the individual life dwells inside this Vijñānamayakośa and pervades the entire body. It is by the activity of Vijñānamayakośa that the Jīvātmā feels its individuality. Inside the Vijñānamayakośa there exists a fifth kośa (chest) called the Ānandamayakośa, which is the immediate covering of Jīvātmā, and which has no sense of individuality. The three Kośas, Ānandakośa, Vijñānakośa and Prāṇamayakośa together is called Sūkṣmaśarīra (the subtle body). It must be remembered that Sūkṣmaśarīra is different from Susūkṣmaśarīra (the minute subtle body). Heart is the abode of the Jīvātmā. Hṛdi (in heart) ayam (this being--Jīvātmā exists). So the name ‘Hṛdaya’ (heart) is meaningful. The Puruṣa (male being), which sits inside the heart or the Jīvātmā is as big as the toe according to the Kaṭhopaniṣad. The Jīvātmā or the Aparabrahman is without beginning. Even from the past which is beyond our thinking crores and crores of Jīvātmans had got into individuals and when the Annamayakośas of the individuals decayed due to death, they abandoned them and entered into new individuals. The author of the Bṛhadāraṇyaka gives an explanation to the question why this Jīvātmā which is as free as air enters the body of man, beast, bird, tree, rock etc. and subjects itself to misery and hardship. “Where does the Jīvātmā originate from? how does it enter this body?” Jīvātmā originates from Paramātmā (the soul of the universe). As the shadow pervades the body of a man this Jīvātmā overshadows this body.” Śrī Śaṅkarācārya expounds it in another way; he says that the Jīvātmā is tied to the body by the imagination or desires of the mind.
Note: 2) Tasya prāṇa eva śiraḥ vyāno dakṣiṇaḥ pakṣaḥ apānaḥ uttaraḥ pakṣaḥ ākāśa ātmā, Pṛthivī puccham. (Taittirīya).]
Note: 1) Ayaṁ puruṣaḥ bhāḥ satyaḥ tasmin antarhrdaye yathā vrīhir vā, yavovā, sa eṣa sarvasyeśānaḥ sarvasyādhipatih. (Bṛhadāraṇyaka)]