15God said to Abraham, “As for Sarai your wife, you shall not call her Sarai, but Sarah shall be her name. 16I will bless her, and moreover I will give you a son by her. I will bless her, and she shall give rise to nations; kings of peoples shall come from her.” 17Then Abraham fell on his face and laughed, and said to himself, “Can a child be born to a man who is a hundred years old? Can Sarah, who is ninety years old, bear a child?”18And Abraham said to God, “O that Ishmael might live in your sight!”19God said, “No, but your wife Sarah shall bear you a son, and you shall name him Isaac. I will establish my covenant with him as an everlasting covenant for his offspring after him. 20As for Ishmael, I have heard you; I will bless him and make him fruitful and exceedingly numerous; he shall be the father of twelve princes, and I will make him a great nation. 21But my covenant I will establish with Isaac, whom Sarah shall bear to you at this season next year.” 22And when he had finished talking with him, God went up from Abraham. (Genesis 17:15-22, NRSV)
What a promise!
What would you think if God told your wife who is 90 will have a son?
We would all probably laugh at that. We don’t see how that can happen.
There are many times when God tells us or shows us God is going to do something and we can not believe it because it has never been done before or we do not understand how it can happen.
But when God makes a promise you can believe it!