An Apology for the True Christian Divinity - Being an explanation and vindication of the principles and doctrines of the people called Quakers

The author of this book, Robert Barclay (1648 - 1690), was an early convert to Quakerism. He spent most of his life's work spreading and defending those beliefs. Because of his literary work and preaching, he was imprisoned numerous times. His An Apology for the True Christian Divinity: Being an Explanation and Vindication of the Principles and Doctrines of the People called Quakers is the definitive statement and defense of his views and an interesting source for historical reference.