The constitution provides a set of rules through which the country is to be ruled and also defines the countries ruling ship, whether it is democratic or anyother, widout constitution the country wont have rules and regulations and probably wud be baseless.
With the help of constitution we can get the centralized governance. 
It is indeed necessary in order to make a system which should be followed by all the citizen of india, and the same constitution will make us aware the consequences if we are not following the same.

To create a discipline, and system oriented governance, and to maintain the same on a daily basis we need the constitution.
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