Full Idea
God is the first reason of things: all that we see and experience is contingent and nothing in them renders their existence necessary.
Gist of Idea
God is the first reason of things; our experiences are contingent, and contain no necessity
Source
Gottfried Leibniz (The Theodicy [1710], p.127), quoted by Franklin Perkins - Leibniz: Guide for the Perplexed 2.II
Book Reference
Perkins,Franklin: 'Leibniz: Guide for the Perplexed' [Continuum 2007], p.20
A Reaction
Perkins presents this as the first step in one of Leibniz's arguments for God. They all seem to be variants of the ontological argument. [His 'Theodicy' is the Huggard translation, 1985] This resembles Aquinas's Third Way.