Still considered essential reading for serious thinkers on religion more than a century and a half after it was written, this seminal work of modern theology, first published in 1845, presents a history of Catholic doctrine from the days of the Apostles to the time of its writing, and follows with specific examples of how the doctrine has not only survived corruption but grown stronger through defending itself against it, and is, therefore, the true religion. This classic of Christian apologetics, considered a foundational work of 19th-century intellectualism on par with Darwin's Origin of Species, is must reading not only for the faithful but also for anyone who wishes to be well educated in the fundamentals of modern thought.

The essays selected here for translation derive largely from Thomasius's work on Staatskirchenrecht, or the political jurisprudence of church law. These works, originating as disputations, theses, and pamphlets, were direct interventions in the unresolved issue of the political role of religion in Brandenburg-Prussia, a state in which a Calvinist dynasty ruled over a largely Lutheran population and nobility as well as a significant Catholic minority. In mandating limited religious toleration within the German states, the provisions of the Peace of Westphalia (1648) also provided the rulers of Brandenburg-Prussia with a way of keeping the powerful Lutheran church in check by guaranteeing a degree of religious freedom to non-Lutherans and thereby detaching the state from the most powerful territorial church. Thomasius's writings on church-state relations, many of them critical of the civil claims made by Lutheran theologians, are a direct response to this state of affairs. At the same time, owing to the depth of intellectual resources at his disposal, these works constitute a major contribution to the broader discussion of the relation between the religious and political spheres.