Chasidut к Ирмеяу 2:35

Not a man in the midst of a cheshbon nefesh should do it in a rushed, off handed way. He should feel as if he is standing trial before the court. That is to say, he needs to reach a real awareness that his body, desires, and very soul²⁹²Nefesh, Ruach, and Neshama, deepening levels of soul. are all standing in judgment. They are not being judged by the Heavenly Court, but by man himself. The more honest he is in his introspection, and according to the degree to which he bows his head before the Almighty whose life is in His hands, the more the One who sits in Judgment will be lenient in His ruling. This is an explanation of what God meant when He said, “Behold I will bring you to judgment for saying, I have not sinned.”²⁹³Yirmiyahu, 2:35 Simply put, when there is judgment below, (and man is honest with himself and his relationship to God’s Law), then there is no judgment above, (for He will suspend the sentence.) ²⁹⁴In my ignorance of Divine court procedure, I ask myself, “could the sentence sometimes be suspended conditionally, and at other times unconditionally?” But regardless of Divine calculations that are hidden from us, it seems that God said to Yirmiyahu that if we claim our innocence, He will then not only have to punish us for negligent actions, but also for lying – to God and to ourselves. However, if we judge ourselves honesty, for better or worse, we know what is incumbent upon us to do, then the Merciful Judge will suspend judgment and give us time to make amends.
The man is taking a candid look at himself and asking himself certain questions. The proceedings of his own evaluation require that he first confronts and accepts his true feelings so as to gain a clear view of his merits and mistakes. He asks himself where he is standing with God. “I know we all accepted the Torah, and continue to do so in every generation, but what about me? Have God and I really come to an agreement concerning … ?” And if he feels he is at all negligent, then he needs humility and bravery. He needs the humility to bow his head before the Almighty One who gives him life and the bravery to take it upon himself to mend his ways.
If you consider the historical context, you can clearly see why the Rebbe was writing this book with such passion. It was and still is in order to save us from punishment.

The worst of evils is self-justification, such that one be righteous in his own eyes. And it is like the verse states (Jeremiah 2:35), "I will hereby judge you for your saying, 'I have not sinned.'" Its cause is a lack of introspection, such that a man not introspect about himself. And even worse than this is when he does not expect greatness from himself, and praises himself in his heart, saying, "I have already introspected, and not found any weighty sins in myself; and that is enough for me." But do you not want to at least be a simple Jew? Do you not need to fulfill the stipulation of the Holy One, blessed be He, which He made with us when we received the Torah - that we can only be Israel in this way. You must demand the greatness and holiness of essential Jewishness from yourself; so do not be righteous in your own eyes. Look for and condemn your shortcoming. Gird your loins and elevate yourself (and see Chapter 3 about this).