Socrates actually gives no explanation at all of the distinction: not being able to understand and not willing to understand; on the other hand, he is the grand master of all ironists in operating by means of the distinction between understanding and understanding. Socrates explains that he who does not do what is right has not understood it, either; but Christianity goes a little further back and says that it is because he is unwilling to understand it, and this again because he does not will what is right. And in the next place it teaches that a person does what is wrong (essentially defiance) even though he understands what is right, or he refrains from doing what is right even though he understands it; in short, the Christian teaching about sin is nothing but offensiveness toward man, charge upon charge; it is the suit that the divine as the prosecutor ventures to bring against humankind.
But can any human being comprehend this Christian teaching? By no means, for it is indeed Christianity and therefore involves offense. It must be believed.To comprehend is the range of man’s relation to the human, but to believe is man’s relation to the divine. How then does Christianity explain this incomprehensibility? Very consistently, in a way just as incomprehensible: by revealing it.
Therefore, interpreted Christianly, sin has its roots in willing, not in knowing, and this corruption of willing affects the individual’s consciousness. This is entirely consistent, for otherwise the question of the origin of sin would have to be posed in regard to each individual.
Søren Kierkegaard, The Sickness Unto Death