VaYera: Don't Look Back
The depravity of Sodom was so monstrous that it was beyond all hope of reformation, and God decreed that the city needed to be destroyed. Angels were sent to save Lot's family - not for their own merits, but for Abraham's sake. The rescuers warned Lot and his family not to watch as the city was leveled. Sadly, Lot's wife did look back, and was turned into a pillar of salt.
Why did Lot's wife need to pay such a heavy price for her curiosity? Why wasn't Lot's family allowed to observe the destruction?
The Misguided and the Incorrigible
Just as there are levels in righteousness, so too there are levels in wickedness. Some unscrupulous people are in fact good souls who came under the corrupting influence of evil people and an immoral milieu. These misguided individuals are receptive to change. If they witness the just punishment of the wicked, their innate goodness is awakened and they are encouraged to return to the proper path.
On the other hand, some evil people are so incorrigibly wicked - hardened criminals, for example - that they cannot be influenced or helped. The only thing restraining their evil excesses is fear of punishment. This was the lowly state of the residents of Sodom, who completely identified with their degenerate ways.
When the incorrigibly wicked witness the downfall of evil, it has the reverse effect on them. It actually reduces the fear that holds their vices in check, since imagined destruction is always more frightening than the actual physical ruin. When they observe havoc and devastation, the truly depraved become less inhibited and pose an even greater menace to society.
Lot's Wife
Lot's family did not deserve to be saved. They lacked moral resolve, and were greatly drawn to the malevolent and degenerate ways of the Sodomites. Only fear of Divine retribution kept their immoral tendencies in check.
Lot's family was commanded not to watch the destruction, in order to maintain their fear of retribution. This fear was the only means by which they could escape the villainy of Sodom. When Lot's wife willfully looked back, she lost some of her fear of punishment. She became like the other residents of Sodom, who were destroyed because they were irredeemably corrupt. Lot's wife shared the severe judgment of her fellow Sodomites - 'brimstone and salt' - as she was turned into an inert pillar of salt, an apt symbol of her immutable and irreparable state of evil.
[adapted from Ein Ayah vol. II p. 250]
