When the cities of Sdom and Amora were about to be destroyed, Lot and his family were commanded (Breisheet 19:17) “Escape for your life; Do not look behind you and do not stay on the plain, run for the mountains lest you be consumed.”
Rashbam brings three reasons for why they were told not to look backwards:
So that they would not have mercy on their daughters and sons in law who refused to leave with them, so that they would not be held up along the way and so that they would not see the angels destroying the city.
When God poured sulphur and fire on the cities, Lot’s wife did not follow the commandment not to look back as it says in Breisheet 19:26 “But his wife looked back from behind him and she became a pillar of salt.”
Why did she look back after already being warned not to?
According to Pirkei De Rebbi Eliezer, she had mercy on her two married daughters who lived in Sdom and she wanted to check to see if they were following the rest if the family out of the city.
Near the Dead Sea, a huge rock was found which is identified as Lot’s wife. In the Shulchan Aruch, Orach Chayim 218:8 the halacha was codified: When you see Lot’s wife one should recite the blessing: “Dayan HaEmet” (Bless God who is the true judge) and in memory of Lot one should recite “Zocher Tzadikim” (Remember the Righteous).
Yesterday, I was driving along the Dead Sea and saw a sign that said “Lot’s wife.” The sign points to a rock formation that looks like a woman. The chances that this rock is actually Lot’s wife are very slim considering that the rock is much bigger than an actual person. Also, over thousands of years the shape of the rock would have probably changed. However, we know that she was turned into a pillar of salt in that vicinity, we just don’t know exactly where. The sign reminds us that the story took place in that area and the Dead Sea was formed by the destruction of Sdom and Amora and that is why to this day nothing will grow there.