Why was there such resistance among the Jews to the gospel? On the one hand, as we’ve seen in the past few chapters, it was because they had misunderstood the place of the law. It was seen as the gate into the kingdom of God, given specifically to their race. But as Paul has hammered home in the past couple of chapters especially, the law has no power AT ALL to bring a person into the Kingdom. Rather, the law was given to expose their need for a righteousness they could not attain on their own. It was given to make them ready for a savior who revealed God’s righteousness. In particular, to make them ready for a savior that somehow could do what the law could not do—make them righteous before God.
On the other hand, the resistance among the Jews was also a result of God’s sovereign plan, which Paul unpacks more in chapter 11. For now, we see that God’s plan was always to include the Gentiles. This would show the Jews two things: It would show them that salvation is by grace (because they were the people who didn’t have any of the privileges Israel had in the Old Testament period), and it would show them that their attempt to enter the Kingdom by keeping the law would never work, and was never meant to work.
Paul dismantle’s this view, because our tendency is to drift back to a form of self-righteous pursuit. This brings with it a host of problems, many of which the atheist community points out as the reason why religion is the greatest threat to the world. They speak of a religion that says, “here’s what you must do to reach God” The problem with this approach is that it fuels self-righteousness, superiority, pride, and racism. So God’s announcement of the gospel in such a way that rejects a Jewish nation that had largely settled on Kingdom citizenship based on their privileges is of necessity. It is in verses 4-5 that we see this things that the Jew held onto so tightly for his privilege.
They are Israelites, and to them belong the adoption, the glory, the covenants, the giving of the law, the worship, and the promises. To them belong the patriarchs, and from their race, according to the flesh, is the Christ, who is God over all, blessed forever. Amen. (Romans 9:4–5 ESV)
So Paul expounds this sovereign choice of God.