As Lot and his family leave Sodom, the Lord’s counsel for them is to not look back and not return; instead, they should “escape to the mountain, lest thou be consumed.” Lot’s wife disobeys this counsel and is turned into “a pillar of salt” when the Lord rains brimstone and fire upon Sodom and Gomorrah.

Genesis 19:17, 24–26

17 And it came to pass, when they had brought them forth abroad, that he said, Escape for thy life; look not behind thee, neither stay thou in all the plain; escape to the mountain, lest thou be consumed. . . .
24 Then the Lord rained upon Sodom and upon Gomorrah brimstone and fire from the Lord out of heaven;
25 And he overthrew those cities, and all the plain, and all the inhabitants of the cities, and that which grew upon the ground.
26 But his wife looked back from behind him, and she became a pillar of salt.

Elder Jeffrey R. Holland said:

“[In] Luke 17:32, . . . the Savior cautions, ‘Remember Lot’s wife.’ What did He mean by such an enigmatic little phrase? To find out, we need to do as He suggested. Let’s recall who Lot’s wife was.

“The story, of course, comes to us out of the days of Sodom and Gomorrah, when the Lord, having had as much as He could stand of the worst that men and women could do, told Lot and his family to flee because those cities were about to be destroyed. ‘Escape for thy life,’ the Lord said. ‘Look not behind thee . . . ; escape to the mountain, lest thou be consumed’ (Genesis 19:17; emphasis added).

“With less than immediate obedience and more than a little negotiation, Lot and his family ultimately did leave town but just in the nick of time. The scriptures tell us what happened at daybreak the morning following their escape:

“‘The Lord rained upon Sodom and upon Gomorrah brimstone and fire from the Lord out of heaven;

“‘And he overthrew those cities’ (Genesis 19:24–25).

“My theme comes in the next verse. Surely, with the Lord’s counsel—‘look not behind thee’—ringing clearly in her ears, Lot’s wife, the record says, ‘looked back,’ and she was turned into a pillar of salt (see verse 26).

“Just what did Lot’s wife do that was so wrong? As a student of history, I have thought about that and offer a partial answer. Apparently, what was wrong with Lot’s wife was that she wasn’t just looking back; in her heart she wanted to go back. It would appear that even before she was past the city limits, she was already missing what Sodom and Gomorrah had offered her. As Elder Neal A. Maxwell (1926–2004) of the Quorum of the Twelve Apostles once said, such people know they should have their primary residence in Zion, but they still hope to keep a summer cottage in Babylon [see Neal A. Maxwell, A Wonderful Flood of Light (1990), 47].

“It is possible that Lot’s wife looked back with resentment toward the Lord for what He was asking her to leave behind. We certainly know that Laman and Lemuel were resentful when Lehi and his family were commanded to leave Jerusalem. So it isn’t just that she looked back; she looked back longingly. In short, her attachment to the past outweighed her confidence in the future. That, apparently, was at least part of her sin.”

(“The Best Is Yet to Be,” Ensign, Jan. 2010, 23–24.)