After the battle, the word of the LORD came to Abram in a vision: “Do not be afraid, Abram. I am your shield, your exceedingly great reward.” Abram is honest with God: he has no child, and his servant Eliezer of Damascus will be his heir. God brings him outside and says, “Look now toward heaven, and count the stars if you are able to number them… So shall your descendants be.”
Then comes one of the most important verses in the Bible: “And he believed in the LORD, and He accounted it to him for righteousness.” Abram did not earn righteousness by works. He believed God's promise, and God credited righteousness to his account. Paul builds his teaching in Romans 4 and Galatians 3 on this very verse. We are made right with God the same way — by faith.
God then confirms His promise with a covenant ceremony. Abram cuts animals in two and lays the pieces opposite each other. In those days, both parties would walk between the pieces, as if to say that the same should happen to them if they broke their word. But a deep sleep falls on Abram, and only “a smoking oven and a burning torch” pass between the pieces. God alone walks the path. The covenant rests on God's faithfulness, not on Abram's.
Ten years pass, and Sarai has still not borne a child. She gives her Egyptian maidservant Hagar to Abram, and Hagar conceives. Trouble follows at once — contempt, harshness and flight. But the Angel of the LORD finds Hagar by a spring of water in the wilderness, tells her to name her son Ishmael, which means God hears, and she calls the name of the LORD who spoke to her, “You-Are-the-God-Who-Sees.” Even when God's people take shortcuts, He sees the hurting and the forgotten.
When Abram is ninety-nine, the LORD appears and says, “I am Almighty God; walk before Me and be blameless.” He changes Abram's name, exalted father, to Abraham, father of a multitude, and Sarai's name to Sarah. He gives circumcision as the sign of the covenant in the flesh, and promises that Sarah herself will bear a son named Isaac at this set time next year. Abraham falls on his face and laughs, but he obeys that very same day.