Generational Promise
Isn't it curious that God used people that had trouble conceiving a child as the line of promise? Abram and Sarai, Isaac and Rebekah, Jacob and Rachel. Generation after generation struggled with this, even after God had started the family line. God healed the women, so they could have sons. God did tell Abraham he would be the father of many nations. And He kept that promise. God performed miracles again and again to keep His promise.
There are several women mentioned in the Bible that had trouble conceiving. Hannah, Elizabeth, Manoah's wife/Samson's mother, and the Shunammite woman are examples of this. God blessed all these women with children, with sons.