According to Foucault, in all societies there is a kind of technique that he calls "techniques of the self" (or "technologies of the self"); these are "techniques that permit individuals to effect, by their own means, a certain number of operations on their own bodies, their own souls, their own thoughts, their own conduct, and this in a manner so as to transform themselves, modify themselves, and to attain state of perfection, happiness, purity, supernatural power" (from his short essay "Sexuality and Solitude"; he elaborates the notion in a much longer essay entitled "Technologies of the Self". Both essays are collected in Ethics: Subjectivity and Truth).
The notion of techniques of the self is interesting enough, but what I find even more interesting is Foucault's application of the notion to Christianity. He first points out that each technique of the self implies some truth obligations such as telling the truth, discovering the truth, and being enlightened by the truth. These obligations are either instrumental to or constitutive of the transformation of the self. He then describes the truth obligations implied by Christian techniques of the self:
Everyone in Christianity has the duty to explore who he is, what is happening within himself, the faults he may have committed, the temptations to which he is exposed. Moreover, everyone is obliged to tell these things to other people, and thus to bear witness against himself... First, there is the task of clearing up all the illusions, temptations, and seductions that can occur in the mind, and of discovering the reality of what is going on within ourselves.
I think most Christians would not disagree with this description. But this is not the interesting part yet. As Foucault goes on:
Second, one must get free from attachment to the self, not because the self is an illusion but because the self is much too real. The more we discover the truth about ourselves, the more we must renounce ourselves; and the more we want to renounce ourselves, the more we need to bring to light the reality of ourselves. This is what we would call the spiral of truth formulation and reality renouncement which is at the heart of Christian techniques of the self.
It is not clear that most Christians would accept these words. They may not see themselves as renouncing their selves, for they, like most human beings, do care about their selves.
What Foucault's characterization of Christian techniques of the self captures is precisely Christians' ambivalence towards their selves --- they both care about and renounce their selves. There is such ambivalence because Christianity is both a salvation religion and a confession religion: one has to care about one's self enough to see the need of salvation, but one also has to renounce one's self as a result of confession. In most cases the psychological condition is just ambivalence, but in some cases it may become so severe that it would not be much of an exaggeration to call it a form of schizophrenia.