Summary: The birth of Isaac in Genesis 21:1-7 teaches us to rejoice in God's faithfulness in fulfilling his promise by miraculously calling Isaac into existence.
When Abraham was seventy-five years old, God called him out of Ur of the Chaldeans to go to the Promised Land, which God was giving to him. God also promised to make of Abraham a great nation (Genesis 12:2). However, the problem was that Abraham’s wife, Sarah, “was barren; she had no child” (Genesis 11:30). So, how could God make a great nation of Abraham when his wife was infertile?
After Abraham arrived in the Promised Land, he continued on to Egypt. When he came back, his nephew Lot separated from him and went to the beautiful Jordan valley. Then God met Abraham and said to him in Genesis 13:16, “I will make your offspring as the dust of the earth, so that if one can count the dust of the earth, your offspring also can be counted.”
After many years of waiting, Abraham complained to God. We read in Genesis 15:2–5, “But Abram said, ‘O Lord God, what will you give me, for I continue childless, and the heir of my house is Eliezer of Damascus?’ And Abram said, ‘Behold, you have given me no offspring, and a member of my household will be my heir.’ And behold, the word of the Lord came to him: ‘This man shall not be your heir; your very own son shall be your heir.’ And he brought him outside and said, ‘Look toward heaven, and number the stars, if you are able to number them.’ Then he said to him, ‘So shall your offspring be.’” This was now the third time that God had promised offspring to Abraham.
When Abraham was eighty-five years old, and his wife Sarah was seventy-five years old, she came up with a different plan. God had promised offspring to Abraham, but he had never clearly stated that the offspring would be with his wife Sarah. In those days, the custom was for the husband to produce children through his wife’s servant. So, Sarah gave her Egypt servant, Hagar, to Abraham so that he could produce a child. The plan worked. Hagar became pregnant, as we read in Genesis 16:15, “And Hagar bore Abram a son, and Abram called the name of his son, whom Hagar bore, Ishmael.” Moses added in Genesis 16:16, “Abram was eighty-six years old when Hagar bore Ishmael to Abram.”
The problem appeared to be solved. Abraham had a son just in time, in his old age. As far as Abraham and Sarah were concerned, God had fulfilled his promise to Abraham, and had given him a child. For the next thirteen years, Abraham and Sarah seemed to be content with the situation.
However, Abraham and Sarah’s plan was not God’s plan. Genesis 17:1a says, “When Abram was ninety-nine years old the Lord appeared to Abram.” Now, for the first time, God made it clear that the promised child was to come through Sarah, as he said in verse 16, “I will bless her, and moreover, I will give you a son by her.” Abraham could not believe his ears! What? A son by Sarah who was ninety years old? And he himself was a hundred years old? Verse 17 says, “Then Abraham fell on his face and laughed and said to himself, ‘Shall a child be born to a man who is a hundred years old? Shall Sarah, who is ninety years old, bear a child?’” Abraham’s laughter was a laugher of incredulity. By now, it was physically impossible for him to have children, and Sarah, although barren, was also far too old to bear children. So, Abraham pleaded with God in verse 18, “Oh that Ishmael might live before you!” But God replied, “No, but Sarah your wife shall bear you a son” (Genesis 17:19a).