It was out of God's great mercy that He chose to deliver Lot and his family out of Sodom before He rained down fire from heaven to destroy all the evil that the two cities have chosen to follow. He didn't have to, because His commitment to Abraham did not include it, but He is a God of great compassion. Sometimes we get frustrated with God exercising His mercy upon our enemies, much like Job and the city of Ninevah. We prefer God's judgement, unless He's raining it down on us, then we are full of the desire for mercy and not justice!
The Bible says in Genesis 19:16 that God delivered Lot because of His mercy or compassion unto him and his family. In another place it says it was because God remembered Abraham, in other words, His covenant with Abraham, and had compassion on something that Abraham cared a lot about.
May we always rejoice with those who rejoice when God shows up in their lives with His great mercy and compassion! Choose Mercy!