Isaac is Born to Abraham and Sarah

God keeps His promises and in Genesis 21, He keeps His promises to Abraham and Sarah as Isaac is finally born to them. Abraham was 100 years old when Isaac was born.

"God has made laughter for me; everyone who hears will laugh with me. Who would have said to Abraham that Sarah would nurse children? Yet I have given birth to a son in his old age." - Sarah

Isaac means "laughter."

Isaac grew and was weaned (v.8). Abraham throws a big party to celebrate Isaac's weaning. According to the Believer's Bible Commentary, Isaac would have been between 2 and 5 years old by the time he was weaned. Ishmael who had been born to Abraham by Hagar would be between 13 and 17 years old.

At the party, Sarah notices Ishmael mocking Isaac (Brothers will be brothers, right?). Ishmael's mocking upset Sarah so she had Abraham send Hagar and Ishmael away.

Sarah's order upsets Abraham because Ishmael is also his son, but God comforts Abraham by telling him that he will make a nation out of Ishmael also because he is Abraham's son but it is through Isaac, God's promised son to Abraham that His covenant will be carried out.

The next morning, Abraham gathered bread and water and sent Hagar and Ishmael away. When the water was all gone, Hagar left her son under a bush because she couldn't watch him die. But God heard their cry and an angel said to Hagar:

"What is the matter with you, Hagar? Do not fear, for God has heard the voice of the boy where he is. Get up, lift up the boy, and hold him by the hand, for I will make a great nation of him."

Then, God provided water for Hagar and Ishmael. God was with Ishmael as he grew up in the wilderness. Eventually Hagar brought him a wife from Egypt.