In The Essence of Christianity-this is the classic 1853 translation of the 1841 German original-Feuerbach discusses the "true or anthropological" root of religion, exploring how everything from the nature of God to the mysteries of mysticism and prayer can be viewed through such a prism. He goes on to examine the "false" essences of religion, including contradictions in ideas of the existence of a deity, and then how God and religion are merely expressions of human emotion. This is essential background reading for understanding everything from Marx's Communist Manifesto to modern apolitical philosophies of atheism.

Band 20 erfasst den Briefwechsel Feuerbachs aus den Jahren 1853-1861, in dessen Mittelpunkt die "Theogonie nach den Quellen des klassischen, hebraischen und christlichen Altertums" (1857) als Vollendung der anthropologischen religionskritischen Theorie und die eigene distanzierte Position im so genannten Materialismus-Streit jener Jahre stehen."

Band 11 schliesst mit den letzten, noch zu seinen Lebzeiten erschienenen Arbeiten Feuerbachs die Reihe der "Kleinen Schriften" ab. Neben neu erschlossenen biographischen Beitragen, einem Nekrolog auf den Arzt und Freund F. W. Heidenreich und Nachtragen zur "Theogonie nach den Quellen des klassischen, hebraischen und christlichen Altertums" von 1857 enthalt der Band vor allem Auseinandersetzungen mit der Philosophie und Ethik Schopenhauers, dem Neukantianismus, mit Hegels Philosophie und Psychologie sowie mit dem mechanizistischen und naturwissenschaftlichen Materialismus."

Feuerbachs "Theogonie" ist die Frucht sechsjahriger Studien, die er im Anschluss an die 1848/49 in Heidelberg gehaltenen "Vorlesungen uber das Wesen der Religion" begonnen hatte. Die Schrift vollendet seine philosophisch-anthropologische Theorie vom Wesen der Religion. Seine Religionsanalyse gelangt hier, unter philologisch meisterhafter Benutzung literarischer Zeugnisse des Altertums, zur Theorie des "theogonischen Wunsches": Die Vorstellungswelt der Religion wird als phantastische gedankliche Schopfung blossen menschlichen Wunschdenkens verstanden, das aus schmerzlich empfundener menschlicher Ohnmacht und Bedurftigkeit im irdischen Dasein entspringt. Damit wird die Religion, gleich welcher Erscheinungsform, ihrem Ursprunge nach als allusionarer Akt der Wunscherfullung begriffen; ihr wird ein ausschliesslich subjektiv-menschlicher Ursprung zuerkannt."

Originally published in 1845, this concise critique formed the basis of thirty later lectures delivered in 1848 by Ludwig Feuerbach, one of Germany's most influential humanist philosophers. In The Essence of Religion Feuerbach applied the analysis expounded in The Essence of Christianity (1841) to religion as a whole. The main thrust of Feuerbach's argument is aptly summed up in the original subtitle to this work: "God the Image of Man. Man's Dependence upon Nature the Last and Only Source of Religion." Feuerbach reviews key aspects of religious belief and in each case explains them as imaginative elaborations of the primal awe and sense of dependence that humans experience in the face of nature's power and mystery. Rather than humans being created in the image of God, the situation is quite the reverse: "All theology is anthropology," he says, and "the being whom man sets over against himself as a separate supernatural existence is his own being."
Feuerbach goes on to argue that the attributes of God are no more than reflections of the various needs of human nature. Further, as human civilization has advanced, the role of God has gradually diminished. In ancient times, before human beings had any scientific understanding of the way nature works, divine powers were seen behind every natural manifestation, from lightning bolts to the change of seasons. By contrast, in the modern era, when an in-depth understanding of natural causes has been achieved, there is no longer any need to imagine God behind the workings of nature: "He who for his God has no other material than that which natural science, philosophy, or natural observation generally furnishes to him . . . ought to be honest enough also to abstain from using the name of God, for a natural principle is always a natural essence and not what constitutes the idea of a God."
Feuerbach's naturalistic philosophy had a decisive influence on Karl Marx and radical theologians such as Bruno Bauer and David Friedrich Strauss. His incisive critique remains a challenge to religion to this day.