Dr. Matt Kuefler writes:
Every one of the Church fathers who spoke on self-castration spoke to condemn it. As I argue in my book, they were working hard to demonstrate the manliness of Christianity within a traditional Roman framework, for the purpose of attracting converts from the male aristocracy, and self-castration did not support that agenda. Nonetheless, most betray a begrudging admiration for the goals of self-made eunuchs: after all, virtually all of the Church fathers were also encouraging men to renounce sex, even while they preferred that it was done, as Ambrose said, "by will" rather than "by necessity." Tertullian, in the same treatise, could both ridicule self-castration by saying: "Can anyone ... be called abstinent when deprived of that which he is called to abstain from?" but also praise those persons, "both men and women, whom nature has made sterile, with a structure which cannot procreate," seeing them as a foretaste of the absence of sexual desire in Heaven. Jerome, while discounting the "girding of the loins" as support for castration, also wrote that "all the Devil's strength is in the loins." In each, an awkward support for the end of castration is joined to a condemnation of the means.
Even through the universal disapproval of self-castration, glimpses can be seen of what might have been an articulated defence of the practice. By reassembling these fragments, I believe that it might be possible to reconstruct a "eunuch theology" of sorts. Certainly such a theology would have made frequent appeal to the Biblical passages that presented eunuchs in a positive light: Matthew and Isaiah, foremost, but perhaps also the "girding of the loins" of John the Baptist and Elijah, and the baptism of the Ethiopian eunuch. Beyond that, advocates of Christian self-castration might have relied on a range of metaphors, drawn from their contemporary society, to augment that positive image. ... Even after the Middle Ages, self-castration returned from time to time. Men of the skoptzy movement of eighteenth- and nineteenth-century Russia castrated themselves, believing still to fulfill the command of Jesus. And most of the male members of the Heaven's Gate cult, found dead in their San Diego home in 1995, had been surgically castrated. Their leaders seem with clothing and hairstyles to have encouraged a genderless existence.
This is just a bit of the historical exploration of the place of eunuchs and “eunuch theology” in Christianity from Kuefler. Christianity today is certainly more “manly” and “masculine,” such that self-castration wouldn’t be very likely. It’s worth reading.