What was the cause then why one was loved and the other hated? Why was it that one served, the other was served? It was because one was wicked, and the other good. And yet the children being not yet born, one was honored and the other condemned. For when they were not as yet born, God said, "the elder shall serve the younger." With what intent then did God say this? Because He does not wait, as man does, to see from the issue of their acts the good and him who is not so, but even before these He knows which is the wicked and which not such. And this took place in the Israelites' case also, in a still more wonderful way. Why, he says, do I speak of Esau and of Jacob, of whom one was wicked and the other good? For in the Israelites' case, the sin belonged to all, since they all worshipped the calf. Yet notwithstanding some had mercy shown them, and others had not.
No one could say that Jacob had conciliated God by meritorious works before he was born, so that God should say this of him.… Nor had Isaac conciliated God by any previous meritorious works, so that his birth should have been promised.… Good works do not produce grace, but are produced by grace.
[AD 407] John Chrysostom on Romans 9:11-13