No, an interview is not mandatory when applying for a Schengen visa. The interview serves as an additional measure to verify the details of your application, assess your travel purpose, and confirm your ties to India.
If you are contacted for an interview, you may be asked questions about the following:
Your travel plans.
Financial situation.
Purpose of visit.
Ties to India.
The goal is to ensure you are a genuine visitor who will abide by the visa conditions.