Rabbi Nachum of Chernobyl often traveled to collect money for a fund for pidyan shvuyim (redeeming Jewish prisoners). While traveling through the city of Zhitomir on one occasion, local authorities imprisoned him for his “criminal” work.

One day an elderly woman wrapped in a shawl appeared near his cell and began to speak: “G‑d tested Abraham by instructing him: ‘Go forth (lech lecha) from your land, and from your birthplace, and from your father's house,’ promising that this would ultimately benefit him. But what kind of benefit can come from leaving everything one has? I don't understand.”

Rabbi Nachum, who realized that this woman wasn't an ordinary person, remained silent.

She continued, answering her own question: “Abraham excelled at helping travelers with lodging, food and drink. But because he had never experienced the distress of leaving the comforts of home, or the turmoil of spending endless days on the road, he couldn't identify with the people he helped. G‑d wanted Abraham to gain a deeper appreciation for his work.”

Rabbi Nachum understood (as he later related to Rabbi Zev Volf, the maggid of Zhitomir) that the elderly woman intended to provide Rabbi Nachum insight into his own situation. Clearly, G‑d had arranged for him to be in prison so that he could better appreciate the value of the work he did raising funds to redeem prisoners.

“And, the woman in the shawl” Rabbi Nachum added, “was none other than Sarah, wife of Abraham.”

Source: Admurei Chernobyl, Klapholtz