19 - Sodom is indeed found to be wicked, in how they treat Lot and his guests. God spares Lot and his daughters for Abraham's sake; He destroys Sodom; Lot's wife turns back and dies. Moab and Ammon are born of incest.
20 - Abraham again seeks to protect God's promise on his own, like in Egypt. God preserves the situation again. Abimelech seems to accept Abraham's rationale for saying Sarah is his sister, and Abraham lives in Abimelech's territory. Here and in chpt 12, the promise of a child through Sarah is in danger of not coming true.
21 - Isaac is born and circumcised when Abraham is 100. Hagar and Ishmael are sent away. On the verge of death, God preserves them. As Abraham grows strong, Abimelech makes a treaty with him. Abraham obtains a well and plants a tree in Beersheba.
22 - God tests Abraham to see if his faith is in the child God has given, or in the God who gave him. Abraham trusts God. God shows He will provide a substitute sacrifice instead of taking us, on the mountain of Moriah (future Jerusalem). Also, Abraham's brother Nahor has had 12 children, and granddaughters (future wife).