The Lord came 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 appointed time God had told him. (Genesis 21:1-2)
As the divine Author of Genesis, it’s like God is saying “I told you so!” Something we as Christians have to learn over and over again is—if God said it, then he will do it. God does what he says, and says what he does. Everything he’s said in the Scriptures, he’s gonna do. God “does not change like shifting shadows” (James 1:17).
So we gotta be very careful when we start comparing God to flakey people like us. Even the non-Israelite diviner, Balaam stated, “God is not a man, that he might lie, or a son of man, that he might change his mind. Does he speak and not act, or promise and not fulfill?” (Num. 23:19) We must be mindful when we take our past negative experiences with others, and then project them on God, believing he’s something similar. Just because others have not kept their word, does not mean God will not keep his.
Abraham had to learn this again and again—God means what he says, and says what he means. This God who called him out of Ur is absolutely faithful to his word. The fulfillment of Sarah’s pregnancy proved to Abraham and Sarah that YAHWEH is 100% trustworthy.
Isaac’s birth had a double blessing to it. The first half was to show God’s faithfulness to Abraham. To do the impossible by giving him an offspring from Sarah. The second half was to show God’s faithfulness to the world. After humanity betrayed God, he said that he would send someone to make things right again (Gen. 3:15). And in keeping with his word, through the line of Isaac was the arrival of that promised Person. And God kept his promise by sending Jesus the Christ, who paid the price for our sins and began the process of renewal.
If God said it, then he will do it. And so, do you know what he’s said in his word? If so, what promises in Scripture can you hold onto right now? It’s not too good to be true. Isaac is your proof. Jesus is your proof! Believe his words.