The biblical understanding of God, however, was based on the idea of the freedom of the Creator, Sustainer, and Judge and included the concept that God could suspend the natural order or break the causal chain through miracles. This led theologians to two specific problems: (1) the attempt to prove the existence of God, and (2) the attempt to justify God in view of both the apparent shortcomings of the creation and the existence of evil in history (i.e., the problem of theodicy). Both attempts have occupied the intellectual efforts of Western theologians and have inspired the highest of intellectual achievements. These attempts, however, often presumed that human reason could define the transcendent. Although theologians creatively addressed the issue, it was often simple Christian piety that served to guard the notion of transcendence, while concentrating on the historical revelation of God in the more accessible instrument of God’s self-disclosure in Jesus Christ.

Efforts to explain the ways of God to humans, particularly in respect to the problem of the existence of evil, are called theodicy. This form of justification of God has addressed profound human impulses and has relied upon strenuous exercises of human reason, but it has also led to no finally satisfying conclusions. The problem, which was already posed by St. Augustine of Hippo and treated in detail by Thomas Aquinas, became of pressing importance in Europe in the Thirty Years’ War (1618–48) and its aftermath. At that time Gottfried Wilhelm Leibniz, who did more than anyone to develop the concept of theodicy, endeavoured to defend the Christian notion of God against the obvious atheistic consequences that were evoked by the critical thinkers of his time. The result of such theological efforts, however, was either to declare God himself as the originator of evil, to excuse evil as a consequence of divine “permission,” or instead—as with G.W.F. Hegel—to understand world history as the justification of God (“the true theodicy, the justification of God in history”). These answers did not always satisfy the Christian experience of faith. Many writers influenced by the Christian tradition have reacted against such justifications, most notably the Russian novelist Fyodor Dostoyevsky in his treatment of the suffering of children in The Brothers Karamazov (1879–80).

The German philosopher Immanuel Kant set the terms for much modern reflection on God’s existence when he challenged the grounds of most previous efforts to prove it. Kant contended that it was finally impossible for the human intellect to achieve insights into the realm of the transcendent. Even as he was arguing this, modern science was shifting from grounds that presumed the nature of God and God’s universe to autonomous views of nature that were grounded only in experiment, skepticism, and research. During the 19th century philosophers in Kantian and scientific traditions despaired of the attempt to prove the existence of God.

During the same period some Western intellectuals turned against the very idea of God. One strand of Hegelian thinkers, typified by the German philosopher Ludwig Feuerbach, attempted to unmask the idea of religion as illusion. To Feuerbach, faith was an ideology designed to help humans delude themselves. The idea of dialectical materialism, in which the concept of “spirit” was dropped by thinkers such as Karl Marx, developed in this tradition. It also characterized religion as “bad faith” or “the opiate of the people,” designed to seduce them from efforts to build a good society through the hope of rewards in a life to come.

At the same time, at first chiefly in Britain, scientific thinkers in the tradition of Charles Darwin hypothesized that evolutionary processes denied all biblical concepts of divine creation. Some dialectical materialists incorporated Darwinian theories in a frontal attack on the Christian worldview. Some Christians contended that this was a perversion of evolution, since certain Christian teachings on divine creation, such as creatio continua (“continuing creation”), were both biblical and compatible with evolutionary theory. At the turn of the 20th century, some thinkers in both Britain and the United States optimistically reworked their doctrine of God in congruence with evolutionary thought.