I don't have a grand unifying thesis on Blumenberg yet. For now I am just collecting extracts and trying to comment on them.
Within the overall framework of a response to the widely accepted secularization theory of the modern world definitively authored by Lowitz, Blumenberg argues that the underlying metaphor of an illegitimate transfer of property fails to register in the actual difference between the Christian age and the modern. The criteria which according to this metaphor which justifies the claim of secularization theory are "the identifiability of the expropriated property, the legitimacy of its initial ownership, and the unilateral nature of its removal" (23-4). The investigation of each of these criteria displays the temporality of tradition in the logic of its interruptions.
Under the heading of the "unilateralness of the removal" we find an account of the self-secularization of eschatology by the logic of its own annunciation, as the source of "worldliness:"
Franz Overbeck wrote that to the Church, the end of this world seemed near only so long as it had not yet conquered a piece of it. But this conquest came too late to repress 'immediate expectation,' to compensate for the great disappointment. It must have been the other way around: The energy of the eschatological 'state of emergency,' set free, pressed toward self-institutionalization in the world. But this does not falsify Overbeck's statement of symmetry: "As long as the Church possesses this piece, it will continue to be interested in the continued existence of the world; if the last piece is ever really endangered, then she will join her voice in the old cry again." (45)
The "property" in question here is eschatology, and according to the secularization theory the notion of progress appropriates this eschatology unilaterally.