Romans 9:12

"For the children being not yet born, neither having done any good or evil, that the purpose of God according to election might stand, not of works, but of him that calleth, it was said unto her, the elder shall serve the younger. As it is written, Jacob have I loved, but Esau have I hated."

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 doth not wait, as man doth, to see from the issue of their acts the good and him who is not so, but even before these He knoweth 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.

The clearing up then of the whole passage, to give the whole sense summarily, is here brought out by that blessed person. But that this may be clearer, let us investigate the things he says also one by one; this knowing, that what the blessed Paul aimed at was, to show by all that he said that God only knoweth who are worthy, and no man whatever knoweth, even if he seem to know ever so well, but that in this sentence of his there are sundry aberrations. For He that knoweth the secrets of the hearts, He only knoweth for a certainty who deserve a crown, and who punishment and vengeance. Hence it is that many of those, by men esteemed good, He convicts and punishes, and those suspected to be bad He crowns, after showing it not to be so; thus forming his sentence not after the judgment of us slaves, but after his own keen and uncorrupt decision, and not waiting for the issue of actions to look at the wicked and him who is not so therefrom.

Here Paul shows that the people who came afterward belonged to the promise after the manner of Isaac.

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.

One was chosen and loved, and the other hated, so that everything might be the work of God and of His election and foreknowledge, and not from works, but from Him who calls.

Third, he sets down the promise, saying, not of works, for no works preceded it, as has been said: but of him who calls, i.e., through the grace of God calling, for it was said to her, i.e., Rebecca, that the elder, i.e., Esau, shall serve the younger, i.e., Jacob. This can be understood in three ways.
In one way, as referring to the persons involved, and then Esau is understood to have served Jacob, not directly but indirectly, inasmuch as the persecution he launched against him ended in Jacob's benefit, as it says in Proverbs: the fool will serve the wise (Prov 11:29).
Second, it can be referred to the people who sprang from each, because the Edomites were once subject to the Israelites, as it says in a psalm: upon Edom I cast my shoe (Ps 60:8). This seems to fit Genesis: the nations are in your womb; the one shall be stronger than the other (Gen 25:23).
Third, it can be taken figuratively so that by the elder is understood the Jewish people, who were the first to receive the adoption of sons, in accord with Exodus, Israel is my firstborn son (Exod 4:22), and by the younger is understood the gentiles, who were called to the Father later and were signified by the prodigal son (Luke 15).
The elder people in this case serve the younger, inasmuch as the Jews are our capsarii (slaves who carried boys' satchels to school), guarding the books from which the truths of our faith are drawn: search the Scriptures (John 5:39).