In Genesis chapter 15 God repeated his promises to give Abram land and a large family. He did this by making a covenant with Abram. But Sarai hadn’t yet had any children. So Abram didn’t understand how God would make his family into a great nation. Even so, Abram believed God’s promise to give him a son.
Abram’s faith pleased God. Abram was made right with God by believing in God. This is also called being made righteous or being justified. God put his covenant with Abram into effect through the sacrifice of animals.
In Genesis chapter 17 God repeated his covenant with Abram. He changed Abram and Sarai’s names to Abraham and Sarah. He explained that his covenant with Abraham’s family would last for ever. The sign of the covenant was circumcision. God’s promise of a son took a long time to happen. Because of this it was hard for Abraham and Sarah to fully trust God.
Abraham had a son with Sarah’s slave named Hagar. Abraham lied to the king of Gerar about his wife Sarah. Sarah laughed and didn’t believe God’s promise that she would have a child. But God made it clear that Abraham and Sarah would be the parents of a son.
The three men who visited them said that their son Isaac would be born within a year. God would continue the covenant through Isaac. Even though Abraham and Sarah didn’t fully trust him, God protected them. He also protected the people close to them. He protected Hagar in the desert and promised to bless Ishmael. He also rescued Lot when Sodom and Gomorrah were destroyed.