Full Idea
Each substance is like a whole world, and like a mirror of God, or indeed of the whole universe, which each one expresses in its own fashion.
Gist of Idea
Substances mirror God or the universe, each from its own viewpoint
Source
Gottfried Leibniz (Discourse on Metaphysics [1686]), quoted by Nicholas Jolley - Leibniz Intro
Book Reference
Jolley,Nicholas: 'Leibniz' [Routledge 2005], p.3
A Reaction
Leibniz isn't a pantheist, so he does not identify God with the universe, so it is a bit revealing that substance could reflect either one or the other, and he doesn't seem to care which. In the end, for all the sophistication, he just made it up.