If a person has an equal number of mitzvos and sins, he is given the opportunity to repent until Yom Kippur. If he repents, he is inscribed for life; but if not, he is inscribed for death (Maimonides, Teshuvah 3:3).
Why should people be condemned if, by Yom Kippur, their mitzvos still equal their sins? If the two exactly balance each other, should they not be judged with mercy?
Rabbi Yisrael of Salant said that the answer is obvious. If people are given the opportunity to repent for their sins, yet still fail to do so, their negligence is a sin so terrible that it outweighs all the mitzvos. While people cannot justify their sins, they can say that the intensity of temptation was overwhelming. As one Chassidic master pleaded, "Almighty God, if You had placed the terrors of Gehinnom before people's eyes and had concealed temptation in books, I swear to You that no one would sin. But You put temptation right before people's eyes and relegated the terrors of Gehinnom to the books, where it exists as an abstraction! Is it any wonder that people sin?"
Still, once the sin has been committed and the temptation assuaged, what justification can there be for not regretting that one has done wrong? Hence, said Rabbi Yisrael of Salant, the seriousness of a failure to repent. Sin may stem from an inherent weakness; neglect to rectify past wrongs constitutes an act of defiance and an attitude of unforgivable, arrogant self-righteousness which cannot be forgiven.