The chapter begins by the Lord appearing to Abraham with three men standing by him (angels). Abraham begged God to allow him to show the men good hospitality. This was custom back then, a persons reputation was widely connected to how well their hospitality was to people, including strangers. We are to learn from this, when we see that a strangers needs need to be met by feeding them or helping them with shelter, if we can help we should. You never know when the next stranger you see who may need food or shelter could be an angel which is why when we see a homeless person asking for money instead of judging them as a fake we should always pray to God and ask God what this person truly needs for help and how we can help them. You may not have money to feed them, but sometimes simply letting them know the truth of the gospel is all thats needed to fix their problems.
As Abraham was hosting these three men, they told him that the Lord was blessing Sarah with a child. Sarah overheard this and couldn't help but laugh and doubt that God could do this sense she was well passed the normal child bearing years of her life. This didn't please God, He didn't want Sarah to mock and doubt Him, He wanted her to believe that He was the most powerful and could make anything happen. Sarah lied when she was confronted about laughing at God's promise, she lied out of fear. Telling the truth can be uncomfortable, but the consequences that follow the act of lying are normally far worse.
The last half of this chapter tells how God said he was to judge Sodom and Gomorah because of how much sin was going on there. Abraham asked God that if their were at least 50 righteous people, would God spare them or punish them with the wicked. God said he would spare the whole town if there were 50 righteous. Abraham continued to ask this question but lowering the amount of the righteous from 50 to 45, all the way down to ten and Gods final response was if there was at least 10 righteous he would spare the whole town. This shows how much mercy God has for his righteous followers