Though in many ways unorthodox and reformist, Tillich was undoubtedly a Christian theologian. His concern was to develop a satisfying Christian theology in the context of an acceptable philosophy. Heidegger’s influence can be seen in Tillich’s existential starting-point in his ontology of beings and being itself. He uses the existentialist motif of ‘nothingness’ in his characterisation of the experience of beings as confronting the nonbeing inherent in our finitude. He opposed himself to any understanding of God that might give the impression of deity as a being among others; God in Tillich’s view had to be understood as ‘the ground of being’ or, to use a not-unfamiliar expression, being itself. The manner in which he spoke of God, with such remarks as, ‘God does not exist. . . . He is being itself beyond essence and existence’, led to some accusations of atheism and pantheism.
Tillich’s best-known work is his three-volume Systematic Theology
(1951, 1957, and 1963), which was based on his Gifford Lectures. His work clearly has an apologetic approach. He characterised theology as ‘the methodical interpretation of the contents of the Christian faith’. That is, the Christian faith had to be interpreted and could only be interpreted by reason. Following Aquinas, Tillich sought to show how revelation could be reconciled with reason, since in the end there could be no insurmountable conflict between the two. His understanding of religion emphasised the importance of symbolism, and he held that reason played the role of interpreting revelation through ‘true’ symbols. ‘True’ symbols were for Tillich an expression of the infinite through the finite. The implications for his Christology were certainly unorthodox, significantly in his view that Christ could not be identified with God in any literal sense, but rather a symbolic revelation from God of what humanity ought to be. Tillich’s work also attracted interest and exerted influence beyond theological readership, most notably in his work on existentialism as expressed in The Courage to Be,
published in 1952.