Full Idea
The Great Beast is the great object of idolatry, the only ersatz of God. …Only one thing can be taken as an end, for in relation to the human person it possesses a kind of transcendence: this is the collective.
Clarification
'ersatz' means an artificial version
Gist of Idea
The collective is the one and only object of false idolatry
Source
Simone Weil (Gravity and Grace [1942], 'Beast')
Book Reference
Weil,Simone: 'Gravity and Grace', ed/tr. Crawford/De Ruhr [Routledge 1952], p.164
A Reaction
[Society as the Great Beast is in Republic Bk 6] She is referring to both fascist and communist states. Weil seems to be a left-wing liberal, with a tendency towards anarchism, because her priority is the individual, not the group.