Reviewing Tillich in terms of content and execution is an exercise in repetition. As one of the foremost theologians of his generation, his work has been analyzed and applied in a variety of contexts and to a variety of ends. Here, I will address the major functions of the first volume of his Systematic Theology as an enduring text by way of four commonly referenced themes: 1) the form and function of apologetics, 2) the idea of God as the Ground of Being, 3) the concept of Faith as “Ultimate Concern” and 4) the face and means of theology. 

Beginning with the form and function of apologetics, it is useful to orient Tillich’s view and use of (both within and against) apologetics. Tillich rails against apologetics as, or oriented toward, the perspective of a “God of the gaps” and argues for apologetics as a positive, rather than the more typical negative/defensive, task. The more typical approach suggests a “common ground” that is often vague and less oriented towards Tillich’s essential criterion for theology, i.e. attention to the ever-evolving needs of the church.

The second and third foci rest in two of the most iconic and broadly-applied ideas featured in this text: the concept of God as “Ground of Being” and as well as the notion of Faith as “Ultimate Concern”. Expanding upon the concept of God as “Ground of Being” to indicate the idea of God as that which “determines our being or not-being—the ultimate and unconditional power of being” [p. 21] expressed via the “structure of being”, and likewise contextualizing “Ultimate Concern” as the unconditional thing that “determines our being or not-being”––Tillich manages to re-envision the remit of Christianity and Christian theology as both a practice and an identity, while also speaking to a broader contextualization of such affiliations as products of their time with room to shift and add nuance to the definitions and understandings of these categories as they grow and change across generations. 

Fourth and finally, a point of both potential concern and possible prescience lies in Tillich’s concept of how theology functions, and his consistent affirmation of Theology as Christian: from the very beginning, in fact, asserting that “theology, as a function of the Christian church, must serve the needs of the church” and that a “theological system is supposed to satisfy two basic needs: the statement of the truth of the Christian message and the interpretation of this truth for every new generation.” [p. 3] While the former assertion may seem exclusionary in the modern era of liberal and/or interfaith theology, the latter points toward the enduring spirit of inquiry, encouraging that spirit across an implicitly broad field of future potentiality. Tillich thus provides one of the most thought-provoking and challenging texts of the 20th century. It is a clear testament to the state of theology in his era with relevance and constructive applicability in the present for what it means to study, practice, and push the theological—broadly construed—toward the ever-expanding bounds of what it can be.