Full Idea
Whatever is, is in God, and nothing can either be or be conceived without God.
Gist of Idea
Everything is in God, and nothing exists or is thinkable without God
Source
Baruch de Spinoza (The Ethics [1675], I Pr 15)
Book Reference
Spinoza,Benedict de: 'Ethics', ed/tr. White,WH/Stirling,AH [Wordsworth 2001], p.14
A Reaction
Presumably atheists are not very good at conceiving, because they don't understand properly. This is the pantheism for which Spinoza became famous, or notorious. Critics said he was a closet atheist.