Full Idea
The entire second part of the 'Logic', the doctrine of Essence, deals with the essential self-positing unity of immediacy and mediation.
Gist of Idea
Essence is the essential self-positing unity of immediacy and mediation
Source
Georg W.F.Hegel (Logic (Encyclopedia I) [1817], §65)
Book Reference
Hegel,Georg W.F.: 'The Hegel Reader', ed/tr. Houlgate,Stephen [Blackwell 1998], p.166
A Reaction
He is referring to his book 'Science of Logic'. I don't really understand this, but that essence 'posits' the unity of a thing catches my attention.