In the climactic warfare of the Mahabharata, Prince Arjuna and his brothers fight their cousins, the Kauravas with Krishna as their charioteer. Faced with the moral dilemma of whether to fight his own and kill them or for dharma (duty), Krishna discusses life and death with him and reveals his Vishvarupa as a theophany.
In chapters 10 and 11 of the Mahabharata, Krishna reveals himself as the Supreme Being and finally shows his Vishvarupa to Arjuna. Arjuna experiences the vision of Vishvarupa with the divine vision that Krishna bestowed on him. The appearance of Vishvarupa is described by Arjuna, while he is witnessing it. This is the origin of this image that has been issued on hundreds of holidays.
Vishvarupa has innumerable forms, eyes, faces, mouths, and arms. All creatures in the universe are part of it. He is the infinite universe, without beginning or end. It contains peaceful and angry forms.
Arjuna describes the Vishvarupa in the Mahabharata
There are two more descriptions in the Mahabharata, where Krishna shows his Vishvarupa. When the negotiations between Pandavas and Kauravas break down, Krishna declares that he is more than human and shows the cosmic form of him to the leader of the Kaurava, Duryodhana and his assembly. He appears with many arms and holds many weapons and attributes traditionally associated with Vishnu. He is seen holding the conch, Sudarshana chakra, gada (mace), his bow, his Nandaka sword. The interior of his body is described as containing various deities (including Vasus, Rudras, Adityas, Dikapalas), sages, and tribes (especially those who oppose the Kauravas, including the Pandavas) in his body. This form is described as terrible, and only people blessed with divine vision could resist sight.
Visvharupa painting in Jaipur 18th century 
Vishvarupa Miniature Painting
The other theophany of Vishnu (Narayana) is revealed to the divine sage Narada. The theophany is called Vishvamurti. The god has a thousand eyes, a hundred heads, a thousand feet, a thousand bellies, a thousand arms, and several mouths. He holds weapons and attributes of an ascetic such as sacrificial fire, a staff, a kamandalu (pot of water).
The name Vishvarupa (viśva “all”, “universe” and rūpa “form”, literally “Fully formed” or “Omniform”) appears first as the name of Trisiras, the three-headed son of Tvastr, the Vedic creator, God who shapes all beings. In the Rig Veda, it is described that he generates many forms and contains various forms in his womb. It has also been used for other deities such as Soma in the Rig Veda, Prajapati in the Atharva Veda, Rudra in the Upanishad, and Brahman in the Maitrayaniya Upanishad. The Atharva Veda uses the word with various connotations, for example, a bride is blessed by Vishvarupa (full form) to be able to be a mother and have a child.
Vishvarupa Siglo 19
There have been various understandings of the Vishvarupa throughout the ages, and it has been given various forms according to the ideological branch of the schoolchildren who study it, but the thing to understand is that Vishvarupa does not actually mean “gigantic multi-armed form”. It all started with the first sculptors of the Gupta and post-Gupta era, faced with the difficulty of portraying infinity and multiple parts of the body in a feasible way. Arjun’s description of Vishvarupa gave the iconographers two options: Vishvarupa as a multi-headed and multi-armed god or all components of the universe displayed on the body of the deity. The first Vishvarupa chose the first, while Buddhist images of a cosmic Buddha were displayed in the other format.
Visvharupa por Vidya Devi and Dhirendra Jha.jpg 
What can be understood is that this form is only shown to those who can see it, and cannot be defined in human terms. That is actually an ignorant western understanding. Vishwarupa actually shows that Krishna shows himself to Arjun as everything in the universe, from the infinitesimal to the infinite, throughout all time. So Krishna shows Himself as the whole, as Saguna Brahman, from the highest Shiva to the lowest atom. Not being able to understand that way, the only way is to put the face of the most powerful in the human mind, god and what better than a god? All the gods. In Gita’s description, Vishwarupa is not just multiple faces, but also multiple shapes that all appear at the same time.
