8This 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 offspring… Paul argues that it is the spiritual offspring of Abraham that is the true Israel; those who believe, by faith, in the promises of God. Hence, if Isaac was the seed, Ishmael was not, and Jacob was the seed while Esau was passed over, it follows that not all of Abraham’s natural descendents are of the True Israel. Paul is also making a comparison to chapter 4:11-18, where Paul states that Abraham is the father of all who believes by faith. This inheritance is not given through the flesh or from the law, but a spiritual inheritance received by having faith on the promises of God.
9For this is what the promise said:”About this time next year I will return, and Sarah shall have a son.”…This quotation comes from Genesis 18:12, the context is God promising that the seed will come forth from Sarah’s womb, foretelling the birth of Isaac. At about this time Ishmael was already born, again further proving that not all of the fleshly seeds of Abraham are of the true seeds of Abraham. It is worth mentioning that Paul seeks to prove that God’s election is not based on the physical seed of Abraham all the way from the Old Testament, reassuring his Jewish readers that he is not teaching something new but that God had always been consistently doing this from the very beginning. This is why Paul exegetes and argues from the Old Testament.
10And not only so, but also when Rebekah had conceived children by one man, our forefather Isaac,… Here Paul turns to the even more poignant example of Jacob and Esau, as if anticipating in the former comparison of Ishmael and Isaac that some might object saying one was conceived by a slave and was done out of true faith. In this case, Jacob and Esau were both of equal standing on a physical level; both coming from the same mother, and were even twins. It is made clear that the fulfillment of the promise is not under the fleshly seed but in the Spiritual.
11though they were not yet born and had done nothing either good or bad—… This coheres with what Paul teaches in the first chapter of Ephesians; that God had predestined his elect from before the foundation of the world. Here also Paul begins to exposit the basis in which the elect are called, and excludes the possibility that it might be in God’s foreknowledge of an individual’s positive response to His calling. The view of God electing those whom he foresaw would positively respond to His call is normally inferred from Romans 8:29. However the word foreknew in this verse had been used before as always the opposite of rejection, therefore it does not signify a mere foreknowledge of a certain individual, but is more of an emphasis of God’s special choice or covenant affection for that individual (consider Gen 18:19, Jer 1:5, Amos 3:2). in order that God’s purpose of election might continue,…Instead the basis of Jacob’s election over Esau rests solely upon the purposes of God, His sovereign will and good pleasure. Not because of works but because of him who calls—…This would cohere with what Paul had just stated, that God’s election is not based upon any sort of works or even foreknowledge of good works. It follows from this that there is nothing in man that could have incited God to elect Him, and the basis of their election rests solely on the mercy of God.
12she was told, “The older will serve the younger.” … This was from the birth account of Rebekah in Genesis 25:23. The Tyndale commentary interprets this prophecy as being related not to the individuals of Esau and Jacob but to their descendents for Esau had never rendered service to Jacob. (182) This interpretation seems plausible, but I would also add that this emphasizes how God’s will is to be done and how it is sovereign over human traditions, and is what He wills will be done.
13As it is written, ”Jacob I loved, but Esau I hated.” Paul confirms, from Malachi 1:2-3 an even stronger testimony of God’s divine will. Jacob received the blessings of the Lord through the kindness of God and not of His own merit at all. By nature, and to our human intuitions, the younger should have served the older, but it was God’s good pleasure to have mercy on Jacob while passing over his older brother Esau.