What is the big deal with NSG membership for India?

Can someone please explain a bit about the Nuclear Supplier’s Group (NSG) and what’s all the news surrounding India’s entry into this ‘elite’ club? And why does China want to oppose this?

As much as I understand, NSG already has 48 members and the group is about accountability with regards to nuclear-related business between countries. Now I don’t get it why India so desperately wants to be part of this group? What advantages does it give us? Clearly there’s something here that China along with its ally Pakistan is opposing our entry. But I fail to see and understand what is that makes this group ‘elite’ and how we benefit actually.