Abraham, Abimelech, and Isaac's Birth

Genesis 20:1–21:34

Genesis 20–21 weaves promise fulfillment together with moral fragility. Abraham repeats a half-truth about Sarah, and Abimelech unknowingly takes her. God intervenes to protect the covenant line before any violation occurs. Then the long-promised child is born: Isaac. Joy is immediate, but household strain returns as Sarah and Hagar conflict over inheritance. The chapter closes with a treaty at Beersheba, showing Abraham navigating both family tension and regional diplomacy under God's care.

The Fear and the Protection

Abraham travels to Gerar and again says that Sarah is his sister. Abimelech takes her into his household, intending to make her his wife.

But God comes to Abimelech in a dream:

"Behold, you are a dead man because of the woman whom you have taken, for she is a man's wife." — Genesis 20:3 (ESV)

Abimelech protests: "Lord, will you kill an innocent people?" He says that Abraham told him Sarah was his sister, and Sarah herself said it. He has not violated her.

God acknowledges his innocence: "Yes, I know that you have done this in the integrity of your heart, and it was I who kept you from sinning against me." God commands Abimelech to restore Sarah and to ask Abraham to pray for him.

Abimelech confronts Abraham, returns Sarah, and compensates the household with gifts. Abraham prays for Abimelech, and God heals him and his household.

Calvin reads Genesis 20 as proof that God's covenant fidelity can overrule human fear and misjudgment without excusing them. Abraham's fear is real, and his deception is wrong. Yet God's protection of the covenant line is more powerful than human failure.

Isaac Is Born

At the appointed time, Sarah gives birth to Isaac. Abraham circumcises him on the eighth day as commanded. Sarah's earlier laughter of disbelief becomes laughter of joy:

"God has made laughter for me; everyone who hears will laugh over me." — Genesis 21:6 (ESV)

The promise that seemed biologically impossible is fulfilled exactly as God said. Many commentators emphasize the timing language: fulfillment is not vague but "as he had promised," underscoring the reliability of divine speech.

The Household Fracture

But joy does not resolve all family tension. As Isaac grows, conflict rises between Sarah and Hagar. Sarah sees Ishmael playing with Isaac and becomes angry. She demands that Abraham send Hagar and Ishmael away.

Abraham is distressed. Ishmael is his son. But God tells him: "Do not be displeased because of the boy and because of your slave woman. Whatever Sarah says to you, do as she tells you, for through Isaac shall your offspring be named." God also promises: "As for the son of the slave woman, I will make a nation of him also, because he is your offspring."

Abraham sends Hagar and Ishmael into the wilderness with bread and water. Hagar wanders, and the water runs out. She places Ishmael under a bush and sits at a distance, unable to watch him die.

But God hears the boy's cry:

"And God heard the voice of the boy, and the angel of God called to Hagar from heaven and said to her, 'What troubles you, Hagar? Fear not, for God has heard the voice of the boy where he is. Up! Lift up the boy, and hold him fast with your hand, for I will make him into a great nation.'" — Genesis 21:17–18 (ESV)

God opens Hagar's eyes, and she sees a well. She fills the skin with water and gives the boy a drink. The scene is painful, but divine provision extends beyond the chosen line. God's care for Hagar and Ishmael remains explicit even while Isaac is designated covenant heir.

The Treaty at Beersheba

Abimelech approaches Abraham because he sees that God is with him. They settle a dispute over wells and make an oath. Abraham plants a tamarisk tree and calls on the everlasting God. The ending portrays covenant faith lived in public agreements and durable witness.

What to Notice

Promise preservation occurs through divine intervention. God protects Sarah in Abimelech's court before any violation occurs. The covenant line is preserved not through human perfection but through God's active protection.
Isaac's birth resolves a long arc of waiting. The promise that seemed impossible is fulfilled exactly as God said. Yet the birth does not remove all family tension.
God's care extends beyond the chosen line. Ishmael is not the covenant heir, but God hears his cry and provides for him. God's providence is wider than the focal covenant line.
Covenant faith is lived in public agreements. Abraham's treaty with Abimelech and his planting of the tamarisk tree show that faith is not private; it is lived in community and witnessed publicly.