Why Kesavanand Bharti Case of 1973 is famous?

The supreme court of India enunciated the doctrine of the basic Structure of the Indian constitution in this case. The honorable Supreme Court held that “There are certain principles within the framework of Indian Constitution which are inviolable and hence cannot be amended by the Parliament. These principles were commonly termed as Basic Structure.”
The case was Kesavananda Bharati v. The State of Kerala and Others. The essence of the judgment was that - It is the basis for the power of the Indian judiciary to review, and strike down, amendments to the Constitution of India passed by the Indian parliament which conflict with or seek to alter the constitution's 'basic structure'.
42nd amendment: The 42nd amendment of the constitution of India was basically to reduce the power of Supreme Court & high courts to pronounce on constitutionality of laws.