Full Idea
It is in the nature of reason to perceive things under a certain form of eternity ('sub quadam aeternitatis specie').
Gist of Idea
Reason perceives things under a certain form of eternity
Source
Baruch de Spinoza (The Ethics [1675], II Pr 44)
Book Reference
Spinoza,Benedict de: 'Ethics, Improvement of Understanding, Letters', ed/tr. Elwes,R [Dover 1955], p.117
A Reaction
A wonderful, and justly famous, remark. If you don't feel the force (and poetry!) of this, you aren't a philosopher. It is not only appealing, but I don't see how it can fail to be true. Try producing good reasons which only have temporary force.