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.
-introduction to Brahma Sutra by ShankaracharyaBrahma Sutras 3.3,
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.
One would find the Virata concept in Jainism too.
Hinduism stack exchange.