When the angels destroyed Sodom and rescued the family of Avrahams nephew Lot from the destruction, they warned these fleeing refugees not to look back upon this destruction. When Lots wife ignored this warning and looked back she turned into a pillar of salt.

The Midrash explains that she was punished measure for measure. When her husband asked her to provide some salt to flavor the meal of his angelic guests she refused and even scolded him for introducing such "corrupt" practices in the utterly inhospitable culture of Sodom.

She sinned with salt and was punished with salt.