Genesis 18:10

Luke 1:13

But the angel said to him, "Do not be afraid Zacharias, for your earnest prayer has been heard. Your wife Elizabeth will give birth to a son and you will name him John.

Romans 9:8-9

This means that it is not the physical descendants [of Abraham] who are God's children, but it is the children [born] according to [God's] promise who are [Abraham's true] descendants.

Galatians 4:23

Now the son [Ishmael], born to the slave woman, was born simply of their natural relationship; but the son [Isaac], born to the free woman, was born in fulfillment of a [divine] promise.

Galatians 4:28

Now, brothers, you [Christians] are children of the promise [made to Abraham. See 3:29] just like Isaac, [Abraham's son] was.

Treasury of Scripture Knowledge

Summary

Genesis 18:10

And he said, I will certainly return unto thee according to the time of life; and, lo, Sarah thy wife shall have a son. And Sarah heard it in the tent door, which was behind him.

Lo, sarah

Luke 1:13

Romans 9:8

Galatians 4:23

Bible References

Lo, sarah

But the angel said to him, "Do not be afraid Zacharias, for your earnest prayer has been heard. Your wife Elizabeth will give birth to a son and you will name him John.

This means that it is not the physical descendants [of Abraham] who are God's children, but it is the children [born] according to [God's] promise who are [Abraham's true] descendants.

Now the son [Ishmael], born to the slave woman, was born simply of their natural relationship; but the son [Isaac], born to the free woman, was born in fulfillment of a [divine] promise.