Hashem offers a gift of the greatest proportions: teshuvah. To paraphrase Rabbi Avigdor Miller, zt”l, with teshuvah, no sin is too large — and without it, no sin is too small. To be effective, teshuvah has certain conditions, and one is that it must be sincere. A superficial confession does not erase sin. Further, Hashem must see that one’s teshuvah is complete; one has not only ceased to sin, but wishes to sin no longer. As sulphur and salt poured down on Sodom, Hashem offered to Lot and his family a final chance to do teshuvah and thus be spared from the destruction. That teshuvah had to be complete: He ordered explicitly, “Do not look behind you.”
“Do not look behind you and do not stop in all the plain; escape to the mountain lest you be destroyed” (19:17).
The admonition “Do not look behind you” was added in order to make Lot eligible for rescue. It came to teach Lot that he needed to cease feeling any regret at leaving the sinful place Hashem had condemned. Lot had “tarried” (19:16), which demonstrated some reluctance to leave; but now he gained awareness of the righteousness of Hashem’s justice and he turned his back forever on his past association with the sinners.
Because they chose to obey Hashem’s will and spurn the sinners, he and his daughters earned the right to be saved. But his wife did not achieve the progress her husband and her daughters achieved. She still harbored some affection for Sodom; and though she continued to hasten away, she looked back. Therefore she did not gain the right to be saved. Those who had a change of heart were saved; she failed to desert completely her old inclinations, and she was lost.
It may be asked: the people in the cities were to be destroyed, but why was the plain destroyed? We read that “the plain of the Jordan, which was watered throughout” (13:10) was the source of the wealth of these cities and the cause of their wickedness. “Behold, this was the sin of Sodom your sister: the haughtiness of satiation of food” (Ezekiel 16:49). Therefore, the plain was destroyed to demonstrate to mankind the lesson “He makes rivers into a desert, and the springs of water into a place of thirst; a fruitful land into a saltfield, because of the evil of those that dwelt there” (Tehillim 107:33-34).
The expression “in all the plain” is parallel to “And Lot chose all the plain” (13:11). This is what became of Lot’s cherished choice, and it was for this that he had forsaken his mentor Abraham. Now Lot could view the devastated salt-desert, where all his possessions had gone lost because he had forsaken the wealth of Abraham’s tutelage for the sake of the wealth he had hoped to gain from the fertile plain.
“And his wife looked behind him, and she became a pillar of salt” (19:26). Lot was walking behind his company to urge them onward. “His wife looked behind him,” which demonstrated her regret at leaving Sodom. Now that G-d had shown His condemnation of the evil cities, it was incumbent upon all to share that attitude, especially in view of the admonition of the messenger (19:17). Thhough physically she was going with her husband, her heart was still in sinful Sodom; therefore she was sentenced to remain there (see 19:3).
Thus one who abandons a sinful way of life or a sinful practice must understand that he should not look back with any longing or with the least interest in his former ways. Lot and his family were taught to regret that they had resided in Sodom, and to uproot from their minds all sentiments of attachment to the wicked city.