Virat/Ishwar is the universe. In Hinduism, there were 2 revelations to rishis(seers of truth)
1) Vedas glorifying Brahman to Gyan Yogis
2) Puranas glorifying Virat to Bhakt Yogis
Yagyavalkya, Uddlaka, Gargi etc, were rishis to whom Brahman was revealed and their experiences became Vedas and Upanishads
Shukhdeva, Prashara, Vyas, Brahma, Narad etc, were rishis to whom Virat was revealed along with all the realms, timelines, 3 guna Prakriti etc., and their experiences became Puranas(like Bhagwat Puran, Vishnu Puran etc., total 18 Puranas).
Just like every soul/causal body is reflection of Brahman, in the same way every gross body is reflection of Virat Himself and all the 14 realms, constellations etc. present along the Meru Mountain of Virat, also exists in Merudand(spine) of every individual. This is explained by Krishna in Bhagwat Geeta and Uttara Geeta
- The Sun, the Moon, and the other Devatas, the fourteen Lokas of Bhur, Bhuvar, etc., the ten directions,East, West, etc., the sacred
places, the seven oceans,the Himãlaya and other mountains, the seven
Islands of Jambu, etc., the seven sacred rivers, Gangã, etc., the four
Vedas, all the sacred philosophies, the sixteen vowels and twenty-four
consonants,the Gãyatri and other sacred Mantras, the eighteen Purãnas
and all the Upa-Purãnas included, the three Gunas, Mahat itself, the
root of the Jîvas, the Jîvas and their Atman, the ten breaths, the
whole world, in fact, consisting of all these, exists in the Susumnã.
[As all outward objects that are cognizable by the human senses are
reflected in the Susumnã Nãdi, therefore the Rsis call this body the
"microcosm". For instance,when you see the sun, moon, or the stars,
you do not actually go near to them in order to see, but you see them
because they are reflected in your Susumnã Nãdi]
- In the heart dwells the Mahar-Loka, the Jana Loka exists in the
throat, the Tapo-Loka between the two eyebrows, while the Satya-Loka
exists in the head.
The same Virat was shown to Arjuna by Krishna
Bg 11.52 — Krishna said: My dear Arjuna, this form of Mine you are now
seeing is very difﬁcult to behold. Even the demigods are ever seeking
the opportunity to see this form, which is so dear.
Bg 11.53 — The form you are seeing with your transcendental eyes
cannot be understood simply by studying the Vedas, nor by undergoing
serious penances, nor by charity, nor by worship. It is not by these
means that one can see Me as I am.
Bg 11.54 — My dear Arjuna, only by undivided devotional service can I
be understood as I am, standing before you, and can thus be seen
directly. Only in this way can you enter into the mysteries of My
Similar description of lokas, time divisions etc., you will find in all Puranas, for example description of various realms described by rishi Prashara in Vishnu Puran. It is clear, that revelations in Puranas happened to rishis inside their bodies, and they were Anubhava(experiences) within Virat, which are often seen down as Smritis or mythological stories.