Starting in the socio-cultural changes associated with the recent proliferation of various post-terms, this essay explores Mattias Martinson’s proposal for a theological response to these developments. Based on Martinson’s Post-Christian Theology and The Cathedral in the Center, the essay sketches a post-Christian theology that attempts to transcend both traditional Christian theology and atheism as a response to a societal situation of widespread disbelief. To address the ambivalence of the post-Christian society, post-Christian theology needs to be open, adaptable, and provisional, characterized by a ‘neither/nor’ and an ‘in-between,’ rather than by strong metaphysical claims. In a second step, the essay investigates the post-Christian Christian church. To this end, the essay develops an ecclesiological heuristic model to examine the ecclesiological implications of Martinson’s proposal. Situating the Christian church in the nexus of tensions between the divine and the human, the past and the future, and the open and the bounded, the essay demonstrates how the post-Christian church breaks with the established ecclesiological thinking about the church, rejecting the divine elements, the normativity of past and future, and the boundedness of the church. The result is a flattened or weakened church that is better described as a post-Christian atheist church.