"One day the older daughter said to the younger, 'Our father is old, and there is no man around here to give us children - as is the custom all over the earth. Let's get our father to drink wine and then sleep with him and preserve our family line through our father.'" NIV translation
Here, we see that Lot's lack of faith (fear) opened a door to Satan. Because they fled, his daughters looked around and did not see any men that could give them a family. Therefore, they decided to sleep with their father which is wrong.
"That night they got their father to drink wine, and the older daughter went in and slept with him. He was not aware of it when she lay down or when she got up." NIV translation
We see that Lot drank the wine and that provided the opportunity for the girls to proceed with their plan. He could have said no and avoided the whole situation but did not.
"The next day the older daughter said to the younger, 'Last night I slept with my father. Let's get him to drink wine again tonight, and you go in and sleep with him so we can preserve our family line through our father.' So they got their father to drink wine that night also, and the younger daughter went in and slept with him. Again he was not aware of it when she lay down or when she got up." NIV translation
The older daughter convinced the younger to do the same thing that she had done and they got Lot drunk the next night. Once again, he had the opportunity to do the right thing and refuse to drink and get drunk but he did not. He had been a part of Sodom & Gomorrah and had probably got used to the partying and didn't think anything of it. This is a picture of what the devil is doing in the world today. We are around so much unholy behavior that we often do not even notice it or its effects on us.
"So both of Lot's daughters became pregnant by their father. The older daughter had a son, and she named him Moab, he is the father of the Moabites of today. The younger daughter also had a son, and she named him Ben-Ammi, he is the father of the Ammonites of today." NIV translation
Now, we see the lasting effects of Lot's decisions. The Ammonites and Moabites became enemies of Abraham's descendants (the Israelites) and their legacy lives on even today. This is a reminder that our faith (or our lack of faith) can have lasting consequences.