For all of the continental rationalists, including René Descartes, Baruch Spinoza, and Gottfried Wilhelm Leibniz, God occupied a large and a systematic place. Much could be made of all that these thinkers owe to medieval theology, but the point is that they were centrally interested in the nature of God and God’s relationship to the natural world. The way in which this problem is worked out by Leibniz has much to do with his solution to other problems. Moreover, there is evidence that Leibniz looked upon himself (to a considerable extent) as a theologian and was most proud of his contributions there. He wished to bring peace between Catholics and Protestants, and his writing had some effect along this line. Particularly, Leibniz wanted to provide rational solutions for traditional theological issues, and he made it his major goal to provide a reconciliation between traditional religious views and philosophical thought through demonstrating their essential harmony.
The Theodicy has a unique place among the classical writing in philosophical theology, for it is one of the first attempts to “justify the ways of God to man” in straightforward and philosophical terms. Previous theological views had dealt with the issue of God’s choice and creation of this particular natural order, but many had bracketed this topic as being beyond rational scrutiny, and few had set out to answer it directly and in detail. Theodicy, the discussion of God’s orderings insofar as they concern human purposes, became a major part of philosophical theology after Leibniz’s treatise.
Leibniz was among those who considered Christianity’s merit to be its rational and enlightened nature, as contrasted with at least some other religions. Along with rationalism went a tendency to minimize the differences in nature between God and humanity. Leibniz shared in this tendency, stating that the perfections of God are those of the human soul, even though God possesses them in boundless measure. Leibniz was also an optimist about the essential goodness of humans and the possibility of their perfection, and it is probably this view of the nature of humanity that more than any other single factor led Leibniz into his “best of all possible worlds” doctrine.