Ever since it was first written, Adriaan Koerbagh’s anti-Christian work, A Light Shining in Dark Places, has been nearly inaccessible. Had it been known during the Enlightenment, it would have been a great inspiration to radical thinkers. However, it was suppressed and the author died in jail. The full text is now available in English. Koerbagh demolishes such Christian notions as the Creator, the Trinity, the divinity of Jesus, heaven and hell, angels, devils and miracles. Instead, he presents a monistic world view in which Nature and God are identical. Theology is a part of natural science. God can only be worshipped by acting rationally. Koerbagh’s rational religion is intended to contribute to a free, peaceful and liberal society.