But it is not as though the word of God had failed. For not all who are descended from Israel belong to Israel,
and not all are children of Abraham because they are his descendants; but "Through Isaac shall your descendants be named."
This means that it is not the children of the flesh who are the children of God, but the children of the promise are reckoned as descendants.
For this is what the promise said, "About this time I will return and Sarah shall have a son."
And not only so, but also when Rebecca had conceived children by one man, our forefather Isaac,
though they were not yet born and had done nothing either good or bad, in order that God's purpose of election might continue, not because of works but because of his call,
she was told, "The elder will serve the younger."
As it is written, "Jacob I loved, but Esau I hated."
What shall we say then? 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 upon man's will or exertion, but upon God's mercy.
Revised Standard Version of the Bible, copyright 1952 [2nd edition, 1971] by the 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. (Revised Standard Version - Holy Bible)