Doctrine of basic structure was evolved by Supreme Court in Keshwanand Bharti Case in 1973 and held that certain principles cannot be amended by parliament under any circumstances. They are outside the purview of amending power of parliament and any law enacted to bypass those principles will be declared null and void.
Of late, political executive contended that a parliament is the representative of the people and therefore has the power to amend any provision of constitution according to will and welfare of people. In India, unlike Britain, Constitution and not parliament is supreme, Even the parliament has to work under the provisions of constitution and shall not trespass its mandate.
Supreme Court held that basic structure include supremacy of constitution, sovereignty, democratic and republican nature of India polity, secular character of constitution, separation of power between 3 organs of government etc. All these features are intrinsic for a democratic, secular setup which is free to exercise in its own capacity. Any political interference for short term gains can jeopardize the security and peace of the country and may compromise the freedom and rule of law.
Many features like sovereignty is necessary for maintaining independence from any foreign pressure, secular character is indispensable for maintaining communal harmony and a sense of brotherhood and fraternity while republic character talks about democratic head of state, separation of power brings about a sense of stability in political, judicial and social life and prevent clash of interest of various organs. Unity and integrity is necessary to counter nay external threat and for the prosperity and welfare of the people. Any legislation which impede upon these provisions must be dealt with iron fist because compromise on the democratic and sovereign credentials may give rise to internal colonialism, suppression of freedom, gross human right violations.
Hence in order to encapsulate, doctrine of basic structure in no way impeded upon parliamentary supremacy rather it substantiated democracy and rule of law and accelerated free, fair and participative parliamentary arrangement. Parliament is still the sole authority to enact laws but it must not act malafide and in biased manner and shall not break the constitutional mandate which is the vision of constitutional makers.