This essay is an attempt to analyze an important decision Brzozowski took at the end of his life, i.e. his late turn towards Catholicism, which, despite his own objections, we should nonetheless call a religious conversion. The main reason why Brzozowski resisted the traditional rhetoric of conversion lies in his often repeated conviction that faith cannot invalidate life, because "what is not biographical, does not exist at all." Brzozowski, therefore, rejects conversion understood as a radical and abrupt revolution of the soul, which annuls everything that happened before, and turns to a model of religiosity ("Catholicism, undoubtedly") which preserves his entire biographical past. In this manner, Brzozowski seeks his own formula of faith, more adequate to the "situation" of the modern man who lives in and through History. I argue that the model of "conversion without conversion" Brzozowski chose as representative of modern man is typically, though avant la lettre, post-secular: closer to the Jewish sources of past-oriented tschuva than to the mystical timelessness of traditionally Christian metanoia. The idea that redemption consists not in a liberation of a pure spirit but in a patient working-through of the universal history of creation is an implicit credo of the whole modern age, first fully articulated by Brzozowski and only later in the writings of Hermann Cohen, Franz Rosenzweig, and Walter Benjamin. Brzozowski emerges as a relatively early precursor of the future post-secular option whose advocates, like the author of The Diary, will not allow themselves to "lose a single moment," either of their lives or the world's history.