The concept of 33 koti devata.
The Vedas refer to not 33 crore Devatas but 33 types (Koti in Sanskrit) of Devatas. They are explained in Shatpath Brahman and many other scriptures very clearly.

“Yasya Trayastrinshad Devaa Ange Sarve Samaahitaa, Skamma Tam Bruhi Katamah Swideva Sah”. ~(Atharva Veda 10-7-13) Which means: with God’s influence, these thirty-three (devta) sustain the world.

The number 33 comes from the number of Vedic gods explained by Yajnavalkya in Brhadaranyaka Upanishad – the eight Vasus, the eleven Rudras, the twelve Adityas, Indra and Prajapati. (Chapter I, hymn 9, verse 2)
They are: 8-Vasu, 11-Rudra, and 12-Aaditya, 1-Indra and 1-Prajaapati.

8. Vasus are: Earth, Water, Fire, Air, Ether, Moon, Sun, and Star. They are called Vasus, because they are abode of all that lives, moves or exists. (also mentioned in Mahabharat, 1/66/18)

11. Rudras: The ten Pranas (Praana, Apaana, Vyaana, Samaana, Udaana, Naag, Kurma, Krikal, Devadutta and Dhananjaya) i.e. nervauric forces which live in the human body. The eleventh is the human soul.

These are called ‘Rudras’ because when they desert the body, it becomes dead and the relations of the deceased, consequently, begin to weep. Rudra means one who makes a person to weep. { also mentioned in Harivansha 13/51-52})

12. Adityaas —the twelve months of a year called Adityaas, they cause the lapse of the term of existence of each object or being. { also mentioned in Mahabharat 1/65/15-16})
1. Indra which is also known as the (all-pervading) electricity, as it is productive of great force.

1. Prajaapati , also called the “Yajna” because it benefits mankind by the purification of air, water, rain and vegetables and because it aids the development of various arts, and in it the honor is accorded to the learned and the wise.

The master of these 33 Devatas is the Mahadeva or Ishwar who alone is to be worshipped as per 14th Kanda of Shatpath Brahman.

To start with, the Rig Veda mentions 3 Gods – Agni, on earth; Vayu in the air and Surya in the sky. However, further in the Rig-Veda itself this number is increased to thirty-three, of which 11 are said to be on earth, 11 in heaven, and 11 in mid-air.

The term ‘trayastrimsati koti’ mentioned in Atharva Veda, Yajur Veda,& Satapatha-brahmana, was misunderstood as 33 Crores. The term koti in Sanskrit has 2 meaning, 1 is ‘supreme’ & the other is Crore. Hinduism has 33 Supreme Gods and not 33 Crore Gods.

Source : https://www.wordzz.com 
Compiled with pictures of Vishwaroopa by various artists.