The soldier trains for war; he learns how to kill his neighbor efficiently. And he learns his art (ideally at least) with a fairly high degree of dispassion and self-possession, that is he learns to fight and kill without anger because he has fostered in himself the virtue of courage.
All this the soldier does not as an end in itself but on behalf of others, his nation, his family and friends, and for those who he will never met and who will in some cases even resent his sacrifice.
The warrior's sacrifice's his life for his nation. Even if he never goes to war, but certainly if he does, he comes to see himself in new ways, as one able and willing to kill. This carries with it a great, almost unimaginable, moral risk. And it is bearing this moral risk that is the heart of his sacrifice.
As with the warrior trained for battle, likewise with the confessor.
When he encounters in others sins that are unknown to him he most find in himself some understanding, some point of convergence between himself, his own struggles and failures, and the life, struggles and failures of the penitent. And he must do this without himself succumbing to the sin that he has newly come to see as a possibility for him. The attentive, self-aware confessor, like the warrior, is only able to do the task set before him by imagining a horror as a possibility for him.
And again, like the warrior, the confessor in each and every confession must proceed in a dispassionate and courageous fashion to face a temptation that he may never before have imagined as possible.
Speaking to the spiritual father, St Nicodemus summarizes the matter in this way:
I tell my own spiritual children and parishioners, that the work of confession—like the work of marriage—is first and foremost a personal encounter. To use the language of the old Latin manuals in sacramental theology, the trust between confessor and penitent is the matter of the sacrament of confession. While trust, to be trust, must be mutual, the weight of that trust is bore by the confessor. It is his obligation not simply to root out sin in his own life, but (having entrusted himself first and foremost to Christ our True God), travel in empathy and compassion with the penitent to those areas of the penitent's life where sin and shame have a hold.
The ascetical struggle of the confessor is, however, not simply to see the depths of human shame—this after all is hardly something unknown to the secular therapist. No the confessor's task, his calling and that which is the teleos of his own ascetical struggles is to point out that it is there, in the darkest place of the penitent's life, that the redeeming, forgiving, and healing Light of Christ is to be found.
The confessor, St John of Krondstat reminds me, is a witness to divine mercy. This requires, as I said above, not only that the confessor root out his own sin but that he recognize that no sin is alien to him since all sin is but itself only a symptom of our common and personal estrangement from God. It is the reality this common estrangement in his own life that the confessor must confront and struggle against again and again each time he hears confession. And it is only in this way, to return to St Nicodemus' advice, that he can hope to heal the penitent's sin.