Could the division into varnas and castes cause the decline of Indian civilization? Why?

Yes. An increase in social mobility became one of the conditions for the development of society. With the transition to capitalism, people received de facto equal rights and opportunities. The person’s personality received relative inviolability and there was an opportunity to change the type of activity. But in Indian lands, people were tied to the roles that were prescribed to them from birth, and many segments of the population are still deprived of rights.

One of the components of a person's success in our time is receiving modern high-quality education, mastering the knowledge, skills and abilities necessary for life in society. A person today needs to study almost all his life, mastering everything new and new, acquiring the necessary professional qualities.