Selection from – Ethics – Part II. On the Nature and Origin of the Mind (Page 8)
Spinoza's Words: (the nature of reason is to view things in the light of eternity)
Corollary II.—It is in the nature of reason to perceive things under a certain form of eternity (sub quâdam æternitatis specie).
Proof.—It is in the nature of reason to regard things, not as contingent, but as necessary. Reason perceives this necessity of things. But this necessity of things is the very necessity of the eternal nature of (Deus sive Natura); therefore, it is in the nature of reason to regard things under this form of eternity.
Comment:
The famous phrase originates here. Sub specie aeternitatus (under the light of eternity) is the way it is usually been noted in many contexts. It means, of course, to have achieved a certain "philosophical distance" from everyday concerns. In his proof Spinoza makes use of previously proved propositions.
The strength of the statement lies in the idea that human reason that can form a concept of (Deus sive Natura) acting through its own essence – which means that natural laws are impervious to human desires. Human reason, divorced from emotions, can understand, and by implication accept, the necessity of things like personal disappointments and even death. Reason shows us that which is personally important shrinks to insignificance in the light of the eternal aspects of things.