What is the purpose behind Indian Constitution (85th Amendment) Act, 2001?

The main purpose behind the 85th Amendment Act, 2001, was to extend the benefit of reservation in favour of the SC/ST in matters of promotion with consequential seniority. The amendment has substituted, in clause (4A) of Article 16 of the Constitution, for the words ”in matters of promotion to any class” the words ”in matters of promotion, with consequential seniority, to any class”.