Question

why was reservation provided for certain castes in india

Answer 1

because all muslims are not allowed of modi for harvesting crops and light in the village

Answer 2

Reservation was there in India since the beginning.

According to historical background, the main reason for reservation in INDIA is Castism.

Its not new in India , these reservations concepts are ancient, we can read about this in ancient books like MANUSMRITI.

Manusmriti and other Hindu literature classified the society in principle into four varnas:

the Brahmins: priests, scholars and teachers.

the Kshatriyas: rulers, warriors and administrators.

the Vaishyas: merchants.

the Shudras: laborers and service providers.

This classification was also one kind of reservation where some people were given every facilities and allowed every privileges while some others where denied almost everything​. This lead to CASTESIM , which is now deep in our roots. People were not ready to compromise on anything related to caste. They were even not sitting together. Therefore some sections of society degraded to lowest living standards while some sections became very prosperous. As the time changes the form of reservation has only change. As India gain freedom few policies were made for the uplifting of backward classes people. These policies due to CASTESIM became politically controversial topics and never left our system because we are still stick to CASTE.

Onces the castism is over , the problem of reservation will be solved automatically

Reservations in government jobs and in educational institutions was started after Independence. This was started as an affirmative action to bring fairness and justice to people who were deprived of this, even shunned, for centuries.

The first level of reservation was 15% for scheduled castes and 7.5% for scheduled tribes. A sunset clause was thought of for this, which means that after a time, the levels will be reduced and ultimately reservations would be eliminated as disadvantaged sections of society became equal.

Unfortunately, subsequent generation of politicians made this into a vote bank. The whole noble purpose of reservation, which was affirmative action, got lost in the din.

The worst period was during the disgraceful reign of V.P.Singh (By the way, the only Prime Minister who stuck on to his seat till he was thrown out by a vote of No Confidence in the Parliament). There was a time when it seemed that 100% of govt jobs and seats in educational institutions will get reserved, till the Supreme Court intervened and maxed the quota at (I think) 50%.

We have the spectre today of casteist leaders clamouring for reservations. Even the Gujjars (who otherwise claim a royal lineage), and the Jats (who are kshatriya) want it. 

The noble spirit, pioneered by leaders like Nehru, Ambedkar, Jyotiba Phule and others has gone away.