Does the Punishment Fit the Crime?
G‑d sends His angels to destroy the city of S’dom but first they are to save Abraham’s nephew Lot and his family. An angel instructs them: “Run for your life! Do not look back nor stop anywhere in the plain.”
The Torah recounts, “His wife peered from behind him and she became a pillar of salt.”
The question can be asked, wasn't that punishment disproportionate to the crime?
Rashi was apparently addressing this issue when he commented on the angel’s instruction not to look back. ”You did evil along with them, and it is only through the merit of Abraham that you are being saved. You do not deserve to see their punishment, while you were being saved.”
In other words, turning Lot’s wife into a pillar of sale was not a punishment for looking back per se but rather it was the punishment she deserved for the iniquity which she shared with the Sodomite people.
But, even so, why was her punishment that she became a pillar of salt?
Blinding Sodomite Salt
Rashi addresses this question as well.  He cites a Midrashic comment that when Lot asked her to give a little salt to their guests she said to him, “Are you trying to introduce this evil custom in this place?” She was thus punished “measure for measure.” Since she sinned with salt, she was punished with becoming a pillar of salt.
Another Midrashic source relates that when the angels came to their house, Lot’s wife went to her neighbors asking them for salt for her guests. Her intention was to alert the evil, inhospitable Sodomite residents that her husband had violated the City’s norm of not welcoming guests into their midst.
There is a requirement that after a meal and before reciting Birchas Hamzon-Grace after the Meal, we wash our fingertips to make sure that no Sodomite salt remains on them.  The danger is that residual salt could cause blindness if it were to touch the eyes. Salt, thus, symbolizes blindness to the needs of others.
The pillar of salt punishment was the Torah’s way of teaching us to distance ourselves from moral blindness; where we cannot see the needs of others.
Today we are on our way out of the blinding and destructive forces of exile, the modern-day Sodom, which cultivates selfishness. The only way to escape exiled blindness is for us to sever our ties with it and never look back longingly. By looking back, Lot’s wife showed that she had strong ties to Sodom and its salt-related blindness.
Don’t Wallow in Grief!
There can be another, psychological explanation for Lot’s wife’s turning into a pillar of salt. When people survive a catastrophic event it is crucial that they do not wallow in their past pain, lest they will become victims of that event.
Jewish law restricts the time we are allowed to mourn for the loss of a loved one; we must grieve for no more than 12 months. We may not consciously engage in activities that induce feelings of sadness and grief beyond the prescribed 12 months. We may not wallow in feelings of grief and sadness.
What is true of an individual loss is equally true with respect to a national loss. On the one hand, we are commanded never to forget the tragedies of the past, such as the destruction of Bais Hamikdash and the atrocities perpetrated against us throughout history culminating with the Holocaust. Those remembrances, however, must be compartmentalized. We cannot allow ourselves to wallow in these tragedies lest they overtake and paralyze us. If we do obsess with these memories, we add ourselves to the casualties.
For us to become emotionally paralyzed by the horrible memories of our nation's suffering during the Holocaust, gives the Nazis and their henchmen a posthumous victory; we, in effect, empower them to destroy our lives decades after they were defeated.
Over the years I’ve heard of American Jews who refuse to perform a Mitzvah, go to Shul, study Torah, etc., because of the Holocaust. Little do they realize that, in his wildest dreams, Hitler—may his memory be obliterated—could not have imagined a “better” outcome. Seventy years after he was gone, his actions still caused Jews to run away from their Jewishness. That was his objective in the first place: to destroy Jews and Judaism. We dare not and must not contribute to the realization of his nefarious and diabolical goal.
Remember the evil of ancient and modern day Amaleks?  Yes!  But to wallow in it so that it demoralizes us and prevents us from growing and flourishing? Absolutely not!
The lesson given above explains the Rebbe’s role in steering Jews away from the danger of becoming victims of the utterly defeated and repudiated Third Reich. After the Holocaust, the spirit of nearly the entire Jewish nation was crushed by the unprecedented devastation of Jews and Jewish life.  The Jewish people were threatened with another devastating blow; becoming delayed victims of the Holocaust.
The Rebbe recognized this existential danger.  He altered the focus of Jewry and infused the Jewish people with an optimistic vision of the future. The Rebbe launched dozens of programs and initiatives to help strengthen Jewish life throughout the Jewish world. The Rebbe was not simply content with Jewish survival. The Rebbe wanted, and continues to want nothing less than continued growth and complete Redemption!
The Rebbe launched many Mitzvah campaigns, getting millions of Jews to engage in a Mitzvah, opened thousands Chabad houses to educate adults and children and declared his goal that not one Jew should be left behind!  During the Exodus from Egypt, our Sages tell us that there were many Jews who did not leave. Unlike that dreadful experience, the Rebbe asserted that every single Jew will emerge from this Exile. The Rebbe set forth to transform a seemingly quixotic endeavor into a practical reality, preparing us for the Messianic Age. All it will take for the Final Redemption to unfold could be one more Mitzvah!
The Moshiach Connection
On a spiritual level we can understand the punishment of Lot’s wife turning into a pillar of salt in a novel way.
The Midrash comments on the words of Psalms, “I found my servant David,” and asks, where was he found? In Sodom!
Many interpret this statement as a reference to the fact that Lot’s daughter bore him a son, whom she named Moab. In turn, he was the progenitor of Ruth, the great-grandmother of King David and the ancestress of Moshiach.
In effect, the entire drama of the destruction of Sodom led to the birth of Moab and involved sowing the seeds for Moshiach and the Final Redemption centuries before there was a Jewish people and millennia before the exile from which we will be redeemedו
This, the 17th century Kabbalist Rabbi Shimshon Ostropoli, explains, is what caused Lot’s wife to look back. Rashi says she realized that Moshiach would descend from Lot.  Reasonably enough, she thought that she would be the one to bear his child, who would be the ancestor of Ruth, David and Moshiach. She thought she had nothing to fear because she assumed that she would live regardless of her looking back, or after Lot. This, then, is the meaning of she looked “after” Lot; she looked to those who would come from Lot.
A Chain Reaction
The above also explains the Torah’s musical trope, or note, on the word(s) “vayismahmah-and he lingered.” This word has a rare musical note attached to it; a shalsheles, which means a chain. Indeed, the shape of this note looks like a chain and sounds like a chain. The work Korban He’ani explains that Lot was not so concerned about his personal safety because he knew, presciently, that a major chain (the Davidic dynasty) would emerge from him; so, he was in no rush to leave S’dom. That is why the angel told him not to look after himself; meaning, his progeny.
Lot’s wife’s error was caused by her tainted vision. She saw into the future but she did not grasp what she saw. In a later parsha in the book of Genesis, we will read that Potiphar’s wife tried to seduce Joseph because she saw into the future that a child from her line would be born to Joseph. She did not realize that the child would be born to her daughter Osnas, whom Joseph married.
Similarly, Korach’s rebellion against Moses was based on a faulty vision of the future. Korach foresaw that he would have a descendent, the prophet Shmuel, who would be compared favorably to Moses and Aaron. How then, he thought, could his rebellion fail when this glorious future awaited him? Alas, his vision was imprecise; Shmuel descended from one of Korach’s sons who repented.
The common denominator of these incidents is a vision tainted by selfish interests.  The vision of Lot’s wife was tainted by Sodomite salt-induced blindness of the needs of others. Her ability to see into the future was severely compromised. The same was true of Potiphar’s wife and later on of Korach; their vision was clouded by their selfish ambitions.
When should we follow prophets or visionaries? Only when their vision is not tainted by Sodomite salt; when they are totally selfless, devoted exclusively to G‑d’s message and possess an unmitigated love for the Jewish people to whom they deliver their prophetic message.
The Rebbe’s Vision
Our Rebbe told us as a prophetic message that the Final Redemption is right in front of us. This message takes Sodomite salt and refines it into the salt that was offered on the Altar in the Holy Temple, as a symbol of G‑d’s eternal love and covenant with the Jewish people.
Salt is a metaphor both for blindness and for an eternal covenant.
Indeed, the Midrashic translation of the Torah, known as Targum Yerushalmi, states that Lot’s wife will remain a pillar of salt until the Resurrection of the Dead. When that time comes the negative metaphor of salt will be transformed into a wholly positive one: the elimination of blindness and death and the beginning of eternal life.