Full Idea
The eyes of the mind … are none other than proofs.
Gist of Idea
The eyes of the mind are proofs
Source
Baruch de Spinoza (The Ethics [1675], V Pr 23)
Book Reference
Spinoza,Benedict de: 'Ethics, Improvement of Understanding, Letters', ed/tr. Elwes,R [Dover 1955], p.260
A Reaction
A wonderful slogan for rationalists! Technically it sounds a bit dodgy, as steps seem to be required for a proof, whereas the eyes of the mind presumably offer a priori intuitions, or clear and distinct conceptions. In essence, he is right.