Genesis 19:26

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The reason why Lot's Wife turned back is never clearly stated. Some say that by looking back at the sinful cities she betrayed her secret longing for that way of life. Deemed unworthy to be saved she was punished like the rest of the cities' inhabitants.
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Other says that she turned only to check if her daughters, who were married to men of Sodom, were coming or not. The direct vision of God consumed her mortal flash and turned it into pure salt.

"But Lot’s wife looked back, and she became a pillar of salt."
Genesis 19:26

In the Bible, Lot's wife is a figure first mentioned in Genesis 19. Her name is not given, but in some Jewish traditions she is called Edith.
In the tale, two angels arrived in the city of Sodom at eventide, and were invited to spend the night at Lot's home. As dawn was breaking, the angels urged him to get his family and flee, so as to avoid being caught in the impending disaster for the iniquity of the city. The command was given, "Flee for your life! Do not look behind you, nor stop anywhere in the Plain; flee to the hills, lest you be swept away."
While Lot's family was escaping on the plain, disobeying the angels' warning, Lot's wife turned back. The sight of God, who was descending down to rain destruction upon Sodom and Gomorrah, turned her into a pillar of salt.

Soundtrack: "Eerie Stealth" from ObadiahBB.