The concept of sin has a very central place in Christianity. The Bible repeatedly refers to it.
And it is supposed to be a pious Christian’s duty to repent for the sins.
This repentance is interpreted in several ways, and there are several ways in which it is advised that the atonement can take place. But obviously, any question of repentance is meaningless without first understanding what the sin is.
Otherwise, there is the absurd situation of a man trying to correct a mistake, without knowing at all what the mistake is?