Genesis Chapter 21
Then the LORD visited Sarah and she became pregnant with Abraham’s child at the exact time He promised them. They called him Isaac, and he was circumcised 8 days after birth. Abraham was 100 years old!
Isaac grew and Abraham had a great feast the day Isaac was weaned, but Sarah saw Ishmael laughing, so she had Abraham cast Ishmael and Hagar out because Ishmael wouldn’t be an heir with Isaac. Abraham was troubled because of his son Ishmael, but God spoke to him and told him to not be displeased and to do what Sarah said to do, because it is through Isaac that Abraham’s offspring will be named (Gen. 21:12). Then He reminded Abraham of His promise to bless Ishmael (Gen. 21:13). So in the morning Abraham gave Hagar and Ishmael some bread and water and sent them away into the wilderness of Beersheba.
After the food and water ran out Hagar feared the death of Ishmael and she cried out to God, and He heard the voice of the boy. So the angel of God comforted her with God’s promise to bless him (Gen. 21:18-19). They did as the angel said and Ishmael grew up in the wilderness of Paran, and Hagar took him a wife from Egypt.
Now, back to Abraham. Abimelech and Phicol (the commander of Abimelech’s army) from the land of the Philistines saw that Abraham was always blessed with success so they made a treaty with him that Abraham would deal honestly and kindly with them as they had with him. Abraham agreed. Abraham admonished Abimelech about a well that his servants took, and he hadn’t heard of it and seemed sorry, and they made a covenant with each other (Gen. 21:27). Abraham gave Abimelech 7 ewe lambs as a witness that Abraham dug the well. This place was called Beersheba. So Abimelech and Phicol went home, and Abraham planted a tamarisk tree in Beersheba and called on the name of the LORD, the Everlasting God, and Abraham sojourned many days in the land of the Philistines.
Here we see God's gracious gift of a son in Isaac, but we see more than that. Again, we see that God is steadfast to keep His promises and we also see that He is completely trustworthy. Who has a child when he's 100 and his wife is 89 or 90? (see Gen. 17:17 for Sarahs' approximate age) Those whom God says will! God is unstoppable in His promise to bless the nations through Abraham, and He is unstoppable to continue the line through which He will bring the Messiah, Jesus Christ. Not only is God being kind to give Abraham a son, but He is being kind ad infinitum in sustaining Eve's seed so that we might all be blessed to be able to be saved through Jesus' atoning work on the cross to justify sinners. I hope as we move through these stories you're seeing that this is relevant to you, because it's the family history of how Yahweh, the one true and living God, brought about a Savior so that we might be reconciled to God!