Indian Varna Vyavastha which is incorrectly called the cast system is just a concept.
The first mention of Brahmin, Kshatriya, Vaisya, and Shudra is in Rig Veda Purusha Sukta Hymn 10.90, Shloka no. 11 and 12.
In 11 Shloka it is written that “when all the Devine Powers imagine a Social Purusha they asked what would be the mouth of this Purusha? What would be like Arms? What would be the middle part of the body and what would be the foot?
In Shloka 12 it is said that Brahman would be the mouth, Arms would be Kshatriya, middle body is Vaisya and foot would be Shudras.
For Referances: http://www.aryasamajjamnagar.org/rugveda_v5/rugveda.htm
Nowhere in the Shlokas term” Verna” or “Class” is mentioned. Here what is mentioned are the parts of a society.
So as per the Vedas Brahmin, Kshatriya, Vaisya, and Shudra are the parts of a society and are not classified under any cast or order.
Saying that the Cast System is mentioned in Vedas is rather controversial than correct.
One of the holiest Book of Hindu Dharma Shrimadbhagwadgeeta or simply “The Geeta” it is written in Chapter 4 verse 13: God Krishna himself says that Brahmin, Kshatriya, Vaisya, and Shudra the 4 Vernas are created by him on the basis of the Karma (Deeds) and Guna (Traits or Characteristics).
So as per Geeta it is clear that the Varna Vyastha was based on Deeds and Traits of the people and they were assigned their work on these basis.
Varna is from the root ‘vri’ which means choice according to inherent traits.
In the present circumstances Indians do not follow this Varna Vyastha but they follow Jati Vyastha which is no were approved in Vedas and in the Holy Geeta.
Difference between Jati and Varna:
The basic difference is that Verna is based on the Characteristics and Jati is by birth. If you are born in a Jati of a Brahmin you will be a Brahmin even if you do not posses the qualities of a Brahmin.
No were in Indian Mythologies and Indian Holy Books Jati Vyastha is approved.
If you are following Jati Vyastha your following of the Hindu religion is questionable.