One day Abram had a vision and he heard God say to him, "Do not be afraid, Abram. I will protect you and reward you." But Abram answered, "O Lord God, what can you give me since I have no children and one of my servants, Eliezer of Damascus, will get my property when I die." Then God replied, "This man will not inherit your property; your own son will! Go outside and look at the stars. Try to count them. You will have as many children as that!" Even though Abram was very old, he still believed God, and so God considered him righteous.
Then God said, "I am the God who led you out of Ur in Babylonia to give you this land." Abram asked, "How can I know it will be mine?" God said, "Bring me a cow, goat, sheep, dove and pigeon," So Abram brought the animals and killed them. He cut the three big animals in half and put the pieces in two rows. Then God said, "Your children will be slaves in a foreign land for four hundred years. Then they will come back here." Suddenly a smoking fire pot and flaming torch appeared and went between the parts of the animals. In that time it was the custom for people to cut animals in half and walk between the pieces when they made an agreement. Then God said, "I will give your children all this land from the Egypt Wash to the Euphrates River."
When Abram had been in the land of Canaan for ten years, he still did not have any children. Now it was the custom in that time that when a rich wife could not have children, she would give one of her slave girls to her husband as a second wife to have children for her. So Sarai said to Abram, "Take my slave girl as your wife. Maybe she can have a child for me." So she gave her Egyptian slave girl named Hagar to him as a wife. But when Hagar became pregnant, she became proud and looked down on Sarai. Then Sarai began to treat Hagar so badly that she ran away.
The angel of God met Hagar at a spring in the desert and said, "Hagar, slave of Sarai, where you come from and where are you going? Hagar answered, "I am running away from my mistress Sarai." The angel of God said, "Go back to her and obey her. I will give you so many children they can not be counted. You will have a son and you will name him Ishmael." So Hagar returned to Sarai and gave birth to a son for Abram when he was 86 years old. And Abram named the boy Ishmael, which means "God hears"
When Abram was 99 years old, God appeared to him and said, "I am God Almighty. Obey me and do what is right. You will be the father of many nations. You will no longer be named Abram but will now be called Abraham [which means, 'the father of many']. I will make an agreement with you and give you and your children this land. As a sign of this agreement every man among you must be circumcised. From now on you must circumcise every baby boy when he is a week old. You must no longer call your wife Sarai; from now on her name is Sarah. I will bless her and give you a son by her." Then Abraham bowed down, but he began to laugh when he thought, "Can a man have a child when he is a hundred years old? Can Sarah have a child at ninety?" He said to God, "May Ishmael be the one that you bless." God replied, "No. Your wife will have a son and you will name him Isaac [that is, 'he laughs']. I will make my agreement with him and his children. I will bless your son Ishmael and give him many children, but I will make my agreement with your son Isaac, who will be born to Sarah about this time next year."
On that same day Abraham had himself and Ishmael and all his men slaves circumcised. He was 99 years old and his son Ishmael was 13 years old. So the Jews continue to circumcise their baby boys as a sign of God's agreement with Abraham to this day.