Question

why is the caste system a central part of hindu religion

Answer 1

The Caste System--(groups assigned by birth not personality). The Hindu conception of the social order is that people are different, and different people will fit well into different aspects of society. Social order or social class according to varna forms the framework of moral duties according to personal characteristics of individuals (not necessarily birth).

Answer 2

There are multiple castes within each of the language groups. For instance a Tamil Brahmin would not like to marry a Gujarati or Hindi non Brahmin, because they belong to lower castes. Actually, the caste system is merely an attempt at social structuring from the old days. You could say it is more of a social or anthropological feature of India. Religion as it is practiticed in Hinduism today doesn't discriminate according to castes. Caste is mostly relegated to when it comes to marriages and little else.

There are stories from Mahabharatha, where Krishna in one of his lilas (divine play) comes masquerading as a chandala (low caste) across a Brahmin in the desert, who is suffering from thirst. But because of his prejudice the brahmin decides not to drink from this low caste person and so loses out on the divine nectar. This story proves that Krishna, who is one of the major divinities in Hinduism, may have been a social reformer.