Hinduism , through its authority called ,Vedas,Rig, Yajur,Sama and Atharva explains the root of the world as Brahman, Reality.

It is The Principle,

Beyond words , Thoughts, Space and Time.

It is Abstract and Subtle.

It is Immanent in everything both Living and non- Living.

It is the Knower ,Known and Knowledge.

It is the Experience,Experincer and the Experienced.

It is the Process and the Result.

Worship of this one Reality which is beyond Attributes is called Nirguna Upasana.

As human nature is limited and would find it difficult to concentrate on The Abstract,Vedas ,as a later development,provide for worship of this Reality beyond Names and Forms, through as a beginning stage,provides for Personal or Individual Deity Worship.

This is called Saguna Upasana.

That is providing Attributes to the Attributes Brahman.

To understand the concept of the Attributeless Reality, the concept of Virata Purusha was developed.

That is the Attributeless Reality is given attributes and are represented in a Single Form.

This Form is called Virata Purusha.

This concept is explained in the Purusha Sooktha.

The exhibition of this Cosmic Form by A Deity is called Viswaroopa.

Lord Krishna exhibits His Viswaroopa in the Bhagavad-Gita.

It is very rare to find the Viswaroopa of Shiva.

Here below is the is the image of Virata Purusha concept of Shiva.

It is not possible for the ordinary man to grasp the Infinite. Therefore the scriptures present various symbols of Brahman, such as Prana, Akasa, and mind, for the beginner to meditate upon. Sometimes they prescribe the cosmic form of Brahman (Vaisvanara) for meditation. These different methods of approaching the infinite Brahman are known as Vidyas or Upasanas.

-introduction to Brahma Sutra by ShankaracharyaBrahma Sutras 3.3,

Further in verse 4.1.5:

(The symbol is) to be viewed as Brahman (and not in the reverse way), on account of the elevation (of the symbol thereby).

Virat is to be viewed as Brahman, Brahman is not to be conceived as Virat. These are means for us to comprehend Brahman. We cannot meditate or conceive of Nirguna Brahman, we can only contemplate Saguna Brahman (Virat). The sky as His head, etc., are means for us to conceive That which is unconceivable. Avângmanasogocharam, meaning that which is incapable of being grasped by word or mind.’

Viswaroopa of Krishna in Bhagavad-Gita.

O Lord of the universe, I see in Your universal body many, many forms-bellies, mouths, eyes-expanded without limit. There is no end, there is no beginning, and there is no middle to all this.

For more follow link for text and Translation.

https://asitis.com/11

One would find the Virata concept in Jainism too.

Reference.

https://hinduism.stackexchange.com/questions/10211/who-is-virat-purusha

Images from.

Hinduism stack exchange.

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