Quite a simple answer..common interest..all our ethnic and linguistic identities cannot in isolation form a nation with the same potential as that of the nation which comprises the current political and geographical extent of India. Therefore it is in our interest to subsume said factional identities to the greater whole- ie. India/Indian. A self evident fact.
Interesting choice of words. That is exactly what we will be required of you when you are asked to give up certain ideas/identity.