When we introduce ourselves we are advertising our origins. Despite some intermarriage among the elites in the cities, Indians still largely remain endogamous, and a Bengali is easily distinguished from a Punjabi. Such differences among Indians often are stronger than what they may have in common. A Brahmin from Karnataka shares his Hindu faith with a Kurmi from Bihar, but the two diverge completely when it comes to physical appearance, dress, social customs, food, language and political objectives. At the same time, a Tamil Hindu would feel that he has far more in common with a Tamil Christian or Muslim than with, say, a Jat from Haryana with whom he formally shares the Hindu religion.
Indian nationalism is a rare animal indeed.
It is not based on geography. It is not based on ethnicity. And it is not based on religion. Indian nationalism is the nationalism of an idea, the idea of an ever-ever land that is greater than the sum of its contradictions. You can be a good Muslim, a good Keralite and a good Indian all at once.