They were asked not to look back but Lot's wife disobeyed. Her heart was with Sodom. She was reluctant to run away from her sinful past and therefore looks back. Our attitudes are important. Though the woman was walking towards safety, in her heart of hearts she liked to stay back in sin. That's why she was punished. She was not punished for what she was doing; she was punished for what she was thinking. We may also do the right things for wrong motives. Our desires and thoughts must be purified. One can walk towards a revival meeting with bad thoughts. God sees the thoughts and attitudes. She was going out of Sodom with Sodom in her heart.