When J.-K. Huysmans set out to write the result of Durtal's conversion to Catholicism and stay in the Trappist monastery at La Trappe in En Route, the result was La Cathedral, but in writing the book, it quickly became clear that there was no way to fit everything into it. So in The Cathedral, Durtal mostly just works out his doubts and confusions in Chartres. That book ended with Durtal actually committing to someone, namely, setting out to visit the Benedictine monastery at Solesme. The final book in the Durtal sequence, L'Oblat, begins with him going to Solesme, and then follows him as he becomes a Benedictine oblate elsewhere, at Val-des-Saints. As with all of the Durtal sequence, there is a heavily autobiographical character to the book, as Huysmans based the book on his own experience, of about two years, at Ligugé; but Durtal, of course, is not Huysmans, and his path, however much it may loosely follow Huysmans's own, is not the same path.
There's been a bit of a Commedia structure to the Durtal sequence, starting with hell in La-bas, and moving to the definitely purgatorial En Route and La Cathedral, so one would naturally expect L'Oblat to be the Paradiso of the sequence, as it has in some ways been set up to be. And perhaps in some broad sense it is (we will see), but there is no true heaven on earth, and the situation in France was complicated. Huysmans himself had finally found a manner of life that brought together his art and his faith, but in the aftermath of the Dreyfus Affair, this was absolutely crushed. In 1901, the Republic passed the Waldeck-Rousseau Law of Religious Associations; Waldeck-Rousseau was a vehement anti-clericalist who had repeatedly tried to pass laws restricting the rights of religious groups, and after Dreyfus he was able to pull together the support required for it. The law, explicitly passed in order to impose the supremacy of the state over the Catholic Church, imposed all regulations for all other associations on religious associations (despite the fact that none had been written for religious associations) and began a massive closure of religious institutions -- schools, hospitals, monasteries -- for not already being in compliance with the newly imposed regulations.
In retrospect, of course, it was one of the early signs of the more general phenomenon of the rise of twentieth-century statism and totalitarianism, but for Huysmans it was more personal, as the abbey that had been part of his daily religious devotion was forced to relocate outside of France, leaving Huysmans little choice but return to Paris, a Paris in which religious institutions had received a maiming blow. What infuriated Huysmans further was what he saw as the widespread failure of French Catholics, and even the Pope, to respond properly to the aggression, which was (deliberately) usually rather minimal. Huysmans saw this as effectively a betrayal, and as he wrote The Oblate began to conceive it not merely as a rebuke to secular Republicans but as one to French Catholics at well. Because of this, some scholars have suggested that the book sets up for a possible future de-conversion of Durtal. Given that Huysmans himself never de-converted, this is immensely unlikely -- and yet we can be sure, just from the circumstances in which it was written, that there can be no ordinary happy ending for Durtal. The closest our world gets to heaven is prayerfully suffering and enduring for the right reasons. Huysmans knew that from experience.
In any case, no further Durtal works were written; after The Oblate was published in 1903, Huysmans only published some works of hagiography and art criticism before his death in 1907.
Continuing Huysmans's application of the techniques of the Naturalist literary school to unusual topics, the book is also famous for having an unusually accurate depiction of turn-of-the-century Benedictine liturgy. We saw as far back as La-bas the influence of the ongoing struggle in Catholicism between different visions of liturgy, a struggle we still see today and sometimes call 'the liturgy wars', and this has been ongoing, if not quite as emphasized through the following books. (One can, however, read The Cathedral in great measure as concerned with widespread French Catholic ignorance of the underlying 'language' of the traditional liturgy.) Durtal's path to the Church, after all, was art, and one of the obstacles to his original conversion was priests (and lay Catholics, but especially priests) substituting for the traditional Catholic arts pop versions that were really just bad, kitschy imitations of the popular arts of contemporary culture. What kept him on the path was a combination of the simplicity of monastic life and the liturgy itself. The liturgy cannot but be a part of his next step in religious commitment.
I will be reading Brendan King's recent translation (2023); I've liked King's translations of the other books in the sequence.