Full Idea
Men who are governed by reason - that is, who seek what is useful to them in accordance with reason - desire for themselves nothing, which they do not also desire for the rest of mankind, and so are just, faithful and honourable in their conduct.
Gist of Idea
Rational people are self-interested, but also desire the same goods for other people
Source
Baruch de Spinoza (The Ethics [1675], IV Pr 18)
Book Reference
Spinoza,Benedict de: 'Ethics, Improvement of Understanding, Letters', ed/tr. Elwes,R [Dover 1955], p.202
A Reaction
This is pulling a rather Kantian rabbit out of a very social contract hat. It chimes in with Aristotle's account of self-interest, which leads to good civic virtues. True Kantianism is self-abnegating, but Spinoza lets selfishness take the lead.