It is well known that Stirner and Nietzsche—first the former—were opposed to Christianity for the paradox contained causally by its demonology. The paradox of Christian life is that one is free insofar as one is a slave (to Christ). It is enough to say that being a slave, in any sense, is improper for the concept of freedom, for Nietzsche. For as he amplified tirelessly by way of a series of enthymemes in his AntiChrist: all that is life denying is bad; all that is life affirming is good. If we string along Nietzsche’s definitional meanings, it seems obvious that he contains a set of propositions that are almost Stoic, or perhaps Epicurean. In Thus Spake Zarathustra, life just means “the instinct for growth, of permanence, of accumulating forces, of power”, while Good just means “all that enhances the feeling of power, the will to Power, and power itself in man.”
For anyone familiar with the therapeutic tradition in philosophical ethics (eu-daimonia) the idea here is that one ought to return to oneself in order to overcome weaknesses. In the Christian monastic tradition the idea is that one ought to return to God in order to overcome weakness. For Nietzsche, of course, this is weakness; and yet, for the Christian, relying on oneself is weakness. Strength is good if supplemented by God; strength is bad and leads to vice if supplemented by anything opposed to God (including the self).
The Christian demonology caught up in mystics like Eckhart, Francis, the desert Fathers, and monasticism would articulate that the meaning of life-affirmation is precisely what’s up for grabs. More specifically, Christian demonology wouldn't take issue with such a distinction between life-affirmation and life-denial, only, it would articulate that true life begins only in the folds of God; for God releases us from death (sin), or more specifically, God releases us from having been abandoned by God. Life affirmation in Nietzsche is precisely to reject the folds of God; and, for Paul, Nietzsche’s trajectory puts us on the way to slavery to sin.
The point is that Nietzsche is rhetorical and depends on already agreeing. Our terms make it impossible to speak. For Nietzsche, the term “life affirmation” is, for the Christian, slavery to sin. For Nietzsche, Christian slavery, which we said was freedom, is obviously “life denial”. How we understand our opponents terms depends on our capacity to relate; and yet the Christian cannot see Nietzsche as having produced a desired concept; and for Nietzsche, the Christian will always appear a fool for Christ. And so it goes, back and forth.
Nietzsche gains the upper hand by keeping his intention closed. The whole rhetorical narrative, powerful as it is, depends on not disclosing freedom. That is, we don’t exactly know what Niezsche means by freedom; but we think that what St. Paul meant was obviously false. That is, we have a concept of God that makes it so that determinism is true in some sense if God is involved as first cause, and that somehow if blind forces and the return of the same are the metaphysical underpinnings of reality, these leave us free(er) to take responsibility. If we live in a moral universe, we have to accept a correspondence theory of moral truths (however hazy); if the world is amoral, if we simply create the law as we see fit, given our perceptual approximation on the common good, nothing stops us from seeing the matter differently, of redescrbiing the moral Good. (And of course, if the latter is what we want, it is not clear how negative theology doesn't give us the same possibilities).
Of course, taking issue with the idea of God in general depends on clarifying concepts of what we take God’s revealed messianic word to be. If we take the Christian word on the messianic to be our desired focal point, the most interesting notions are those that are spelled out in his beatitudes. The most promising conception of the messianic Christ is the word against punitive justice (Matthew 5:38-42): not returning evil for evil, but good for evil. Thus while we are told to refrain from stealing (because the promise is that such is failing to trust God—and so, how often do we fail to not idolize in how we make our own plans, thereby fail to have faith), if someone steals from us, we are to give more; to see to their needs independently of the punitive aspects of the law. Imagine the insanity of having someone break into your house and you send them on their way with more, or you let them take and you go further and cook them a meal. Such is the radicality of mercy and forgiveness in opposition to the evil of punitive justice.
The Christ here would make us indifferent to our things, indifferent to the vicious desire for retribution and wrath—which can easily get out of hand and become something very undesired, indifferent to revenge, perhaps; all this in order to seek out a transformative moment, whereby everyone involved is altered according to a different economy. This is slavery to producing the good with the help of divine assistance in the in-breaking messianic word that fulfills the law. Slavery to sin would be to follow the world. Slavery to Christ is far more than simply following a set of rules. How the messianic word operates in hearts is unwritten and non-legalistic. Such is why it is Messianic. And yet it, too, starts from a kind of character.
Let us say that one is never absolutely bound by vices or virtues; and yet that we are bound by our characters. (Aquinas never tires of reminding us that one moment of vicious behaviour doesn’t destroy the character that one has.) It would seem to follow, then, that while one is not bound to do X, one might be likely given to a predictable character. Given this naturalist outlook, it is hard to see what God has to do with our being such that we are. By way of choices and decisions, we have come to develop moral habits, upon which we are ready and disposed to act, but not necessarily. Thus, prima facie, that idea that we are slaves must have something to do with the likely disposition to act. The Christian prediction is that if we follow our own desires, continuously rejecting God, we will harden our characters (developing hardened hearts), and our own drives will be lost for their uniqueness insofar as they fall under the yoke of the World. Never completely, of course.
In Christian freedom, the messianic existence, how the word lives in us, implies that one is predictable perhaps at the beginning of the act, or at the outset; and yet how these words operate in love is unspecified; for the infusion of the supernatural theological virtues (faith, hope and love) open us to a world that is curious. The everyday Christian that doesn't spend time defining how Christian life is better and opposed to the life of the world will not experience the infusion of these virtues. Christianity will always remain legalistic and very much of and in the world. Paul was a willing servant (slave) of Christ because he espied that the world had nothing to offer in comparison to the taste of God and the messianic inbreaking in its overall crescendo; and by this he meant he wished never to choose otherwise than God, making himself always nothing (Paulos) (cf. Agamben, The Time That Remains). The infusion of the supernatural gives the capacity to become otherwise than what is predictable given the world. Does it make us predictable otherwise? Is this not necessarily a legalistic question?
A lot of what Christ says is negative and defined in opposition to what is expected from human characters structured according to the world. It would be a mistake to see the economy of God as a similar kind of thing because the legalistic repetition of Christ’s life (memesis) is only the starting point; the ends to which we are suffused in willful submission to God bring us forever outside, into the open, into freedom from Worldly desires that bog us down and make us incapable of making a unique event.
Uniqueness is always retained in the freedom to reject what our characters, or what our bodies dictate. The desire to be independent of the yoke of God says nothing to the problem of being thereby yoked to the world—Nietzsche’s blindspot. From this angle, it would seem that monastic Christianity is evidently iconoclastic in the messianic question: What does this living word do?—What life is it capable of?