Tractatus Theologico-Politicus

Spinoza's 1670 treatise — published anonymously — arguing for freedom of thought and expression, using biblical criticism to show that Scripture was written by humans for human purposes, and that the only legitimate purpose of religion is to promote justice and charity, not metaphysical doctrine.

Founded modern biblical criticism — demonstrating that the Bible's contradictions and anachronisms show it was authored by multiple humans over time — and argued for the separation of philosophy and theology, making him the first to provide a secular philosophical basis for religious liberty.