Meanings of very keystone in English

For I so admired Hegel's powerful mind that it seemed to me he was the very keystone of all philosophical thought.

This is the very foundation of all social order, rule, and government, and to relax it is to loosen the very keystone of society.

I was fortunate in securing at Melbourne everything I needed except a set of Becquerel ray condensers-butthese were the very keystone of my equipment.