It shows the general purpose behind the provisions of the constitutions. However, it is non-justifiable and non-enforceable by courts. It is derived from the Objectives Resolution proposed by Jawaharlal Nehru in the constituent assembly.
It has amended once by the 42nd amendment  to add the words “socialist” and “secular” were added between the words “Sovereign” and “democratic” and the words “unity of the Nation” were changed to “unity and integrity of the Nation”.
Features of the Preamble of India
Sovereign – This means that India is an independent country and not a dominion of others. Free to acquire and cede its territory to another foreign country.
Socialist – Indian version of socialism is democratic socialism unlike communism socialism i.e. involves nationalization of industry and abolition of private property. In democratic socialism, the public and private sectors exist side by side. The aim is to eradicate poverty, injustice, and inequality of opportunity. Indian socialism is a blend of Marxism and Gandhism leaning towards Gandhism.
Secular – All religions irrespective of strength are having same status and support from the state.
The democratic – Supreme power is with the people. In India, we have indirect democracy where representatives of the people exercise power on their behalf. Indian democracy has social, political, and economic democracy. Direct democracy is in Switzerland. Its devices of it are referendum, initiative, recall, and plebiscite.
Republic – It means that the head of the state is not hereditary. Also, the supreme power is vested in the people and there is no privileged class i.e. all offices are open to all without discrimination.
Justice – This is of three forms Social (All are treated equally with discrimination), Political (All have access to all offices and equal voice in government), and economic (No discrimination on grounds of economic factors)
Liberty – Absence of restraints on activities of individuals and also providing opportunities for the development of individual personalities.
Equality – Absence of special privileges to any section and provision of opportunities for all without discrimination.
Fraternity – Through single citizenship promote a feeling of brotherhood irrespective of caste, religion, sex, creed, and race. It means that the state has to ensure unity and integrity of the nation along with the dignity of the individual.