“God saved you by his grace when you believed. And you can’t take credit for this; it is a gift from God. 9 Salvation is not a reward for the good things we have done, so none of us can boast about it.” Eph. 2:8-9
Abraham was 100 – so he couldn't take any credit for it.
Sarah was 91 and barren – so she too couldn't take credit for it.
It was a gift of God.
You see, if Sarah was strong, if Sarah was young and beautiful, if it was Hagar that the promise came through, we would have no gospel at all.
We wouldn’t have this hope, of God’s strength in our weakness.
All we’d have is, work hard, do better; oh, and if you’re old, and weak, and barren, and empty like Sarah, there’s no hope for you!!
But that’s not all we have is it? No, we have the gospel.
We don’t just have the voice of Ishmael, we have the voice of Isaac. We don’t just have Hagar whispering in our ear, we have the voice of Sarah.
This is why Paul is saying, Sarah represents the heavenly Jerusalem, that’s where you call home. She’s the free woman, and she’s your mother, not Hagar.