Ein Beitrag zur Geschichte der Aufklarung (Berlin, 1888); and E.
The Aufklarung, with its rational theology, was to him the type of abstraction.
It deserves to be noted here that the former, the theology of the Aufklarung, was, like that of the deists, destined to a short-lived notoriety; whereas the solid, accurate and scholarly researches of the rationalist critics of Germany, undertaken with no merely polemical spirit, not only form an epoch in the history of theology, but have taken a permanent place in the body of theological science.
As a distinct movement Pietism had run its course before the middle of the 18th century; by its very individualism it had helped to prepare the way for another great movement, the Illumination (Aufklarung), which was now to lead the world into new paths.
Henceforward he took a deep interest in modern history and politics, as well as in theology, and published Geschichte der Politik, Kultur and Aufklarung des 18ten Jahrhunderts (4 vols.