Through a gradual process, this story became a massive encouragement, with God showing us that this is about far more than Abraham having a son.
Now the Lord said to Abram, “Go from your country and your kindred and your father's house to the land that I will show you. 2 And I will make of you a great nation, and I will bless you and make your name great, so that you will be a blessing. 3 I will bless those who bless you, and him who dishonors you I will curse, and in you all the families of the earth shall be blessed.” (Genesis 12:1-3, ESV)
God’s promise involves Abram having a child but the child is not the focus of the promise. The focus is much bigger; a great nation, a community of God’s people, blessed to be a blessing to all the families on the earth.
In the short term God was creating the nation of Israel who were to bless those around them. But the ultimate fulfillment of this promise is Jesus. One of Abram’s descendants will be God’s own Son, and that is the blessing for everyone on the earth.
This promise involves Abram’s offspring but it is primarily about God’s offspring. Like Abram, Jesus also left his Father’s house to go out into a foreign land. Jesus is the one that is now gathering a community around himself made up of every tribe, tongue and nation. He is the one that has the name above every other name but chooses to bless others, and in him everyone on earth can be blessed.
This story shows that God is able to overcome infertility and give someone a child. But it's about so much more than that. It shows that nothing, including infertility, is able to stop God’s plan of salvation.
Abraham’s story comforted us in our infertility. But the comfort is not necessarily drawn from the promise of God giving Abraham his own child, because I am not Abraham. The comfort comes from the promise of THE child. God has given us the greatest gift possible, the gift of his own son.