Abraham was a hundred years old when his son Isaac was born to him

 Genesis 21:1-34

Now the Lord was gracious to Sarah as he had said, and the Lord did for Sarah what he had promised. Sarah became pregnant and bore a son to Abraham in his old age, at the very time God had promised him. Abraham gave the name Isaac[a] to the son Sarah bore him. When his son Isaac was eight days old, Abraham circumcised him, as God commanded him. Abraham was a hundred years old when his son Isaac was born to him.

But Sarah saw that the son whom Hagar the Egyptian had borne to Abraham was mocking, and she said to Abraham, “Get rid of that slave woman and her son, for that woman’s son will never share in the inheritance with my son Isaac.”

The matter distressed Abraham greatly because it concerned his son. But God said to him, “Do not be so distressed about the boy and your slave woman. Listen to whatever Sarah tells you, because it is through Isaac that your offspring will be reckoned. I will make the son of the slave into a nation also, because he is your offspring.”

God heard the boy crying, and the angel of God called to Hagar from heaven and said to her, “What is the matter, Hagar? Do not be afraid; God has heard the boy crying as he lies there. Lift the boy up and take him by the hand, for I will make him into a great nation.” Then God opened her eyes and she saw a well of water. So she went and filled the skin with water and gave the boy a drink.

 Abraham set apart seven ewe lambs from the flock, and Abimelek asked Abraham, “What is the meaning of these seven ewe lambs you have set apart by themselves?”  He replied, “Accept these seven lambs from my hand as a witness that I dug this well.” So that place was called Beersheba, because the two men swore an oath there.

Abraham planted a tamarisk tree in Beersheba, and there he called on the name of the Lord, the Eternal God. And Abraham stayed in the land of the Philistines for a long time.

Why?

It looks unfair for two families, one stayed at home, and the other has gone away. But here is the way of the Lord, both are blessed by the Lord. There are two countries in the future. They will wage war against each other. 

The Lord always arranges our enemies around us to let us learn a lesson from them. Same as we may have many troubles, we can learn the wonder of the Lord from trouble and suffering.

How?

Blessed is the one accepts the suffering and troubles but still obeys the word of the Lord