This means that it is not the children of the flesh who are the children of God, but the children of the promise are counted as descendants.
For this is what the promise said, "About this time I will return and Sarah shall have a son."
Nor is that all; something similar happened to Rebecca when she had conceived children by one husband, our ancestor Isaac.
Even before they had been born or had done anything good or bad (so that God's purpose of election might continue,
not by works but by his call) she was told, "The elder shall serve the younger."
As it is written, "I have loved Jacob, but I have hated Esau."
What then are we to say? Is there injustice on God's part? By no means!
For he says to Moses, "I will have mercy on whom I have mercy, and I will have compassion on whom I have compassion."
So it depends not on human will or exertion, but on God who shows mercy.
For the scripture says to Pharaoh, "I have raised you up for the very purpose of showing my power in you, so that my name may be proclaimed in all the earth."
So then he has mercy on whomever he chooses, and he hardens the heart of whomever he chooses.
New Revised Standard Version Bible, copyright 1989, Division of Christian Education of the National Council of the Churches of Christ in the United States of America. Used by permission. All rights reserved. (New Revised Standard Bible Version Online)