They explained to him that Nachum the thief was indeed a thief and deserved to remain in prison for a long time, but he insisted. Finally, Rebbe Menachem Mendel managed to reach the judges and told them: "I take responsibility for Nachum that he will not steal again, I am adopting him." The judges were convinced and released Nachum along with him. Immediately upon leaving the prison, Rebbe Mendel took Nachum with him to the Maggid of Mezritch. They traveled to the Maggid, and there Nachum became a devoted disciple of the Maggid, and one of the tzaddikim of the Chasidic movement.
Rebbe Menachem Mendel is likely the first among the Chasidic tzaddikim to be characterized by what later became a sort of "chasidic custom": to be imprisoned due to false accusations. In essence, for everyone who sits in prison, there is always such a "Nachum", a divine reason for which the entire imprisonment, with all its hardships and complications, was worthwhile.
The prison, one could say, is a place where ba’alei teshuvah (penitents) stand. Completely righteous individuals cannot stand there, but Rebbe Menachem Mendel, a man of humility, who after moving to the Land of Israel even signed his letters as "the truly lowly," merited through his humility to be there and thus bring Nachum closer to God. For how does one bring such a Jew, who seems so distant, closer? Only through the power of humility can one see the unique virtue in every Jew and sense his existing closeness to God and consequently illuminate this point within him. Thus, explained the Alter Rebbe, a follower of Rebbe Menachem Mendel’s "prison custom"—he too was falsely imprisoned, twice—that the tzaddik is like a lever: he lowers himself beneath the lowest level, and thereby raises the entire structure.
In fact, one could say that this lever itself is also the point of light within the various “underworld” characters sitting in prison. They sense the injustice and lack of righteousness in the seemingly-ordered world outside, the one run by the establishment, and in a kind of rebellion or protest, they descend beneath it with a hidden desire, as the Rebbe says, "to turn the world over today!" and lift it up.
Even when the wicked break the boundaries of society (and of course, there is such wickedness inside each of us), there is light to be found in the chaos they cause. It is a great light with no vessels capable of containing it. When evil encounters a tzaddik, or the inner tzaddik within each of us (for "your people are all righteous"), the tzaddik is able to elevate the underworld character to holiness and insert his lights of chaos into the broad vessels of the world of tikkun (rectification).
It's also interesting to note that when the Rebbe Rayatz established the daily study known as Chitat (Chumash, Tehillim, and Tanya), the Chitat portion for Rebbe Mendel's day of passing (in a regular year) is the section in Tanya about Rabbi Elazar ben Durdaya, the teacher of all penitents. He too reached the lowest place in the lowest world and emerged from there, and in his merit, and in the merit of those like him, the redemption will come.
