Full Idea
Being in the sense in which it is an object of speculative thought is that which is purely and simply unmediated, that is, undetermined; in other words, there is nothing to distinguish and nothing to think of in being.
Gist of Idea
Being is what is undetermined, and hence indistinguishable
Source
Ludwig Feuerbach (Principles of Philosophy of the Future [1843], 26)
Book Reference
Feuerbach,Ludwig: 'The Fiery Brook: Selected Writings', ed/tr. Hanfi,Zawar [Anchor 1972], p.213
A Reaction
This sounds remarkably like the idea of 'prime matter' used in scholastic Aristotelian philosophy. Matter existing without form is somehow ungraspable, but presented from Hegel onwards as the ultimate mystery.
Related Ideas
Idea 15771 Primary matter is what characterises other stuffs, and it has no distinct identity [Aristotle]
Idea 16589 Prime matter lacks essence, but is only potentially and indeterminately a physical thing [Auriol]
Idea 16571 Prime matter is exceptionally obscure [Zabarella]