As a Lutheran I do not necessarily share the same Covenantal Theology as the Reformed do.
As it pertains to Romans 11, I try to read the chapter within the larger scope of Paul’s thesis in the epistle. The Apostle having established in the early chapters that whether Jew or Gentile, all are sinful and have fallen short of God’s glory–the bondage of sin and death is something all people have because all are born into this world bearing the scars and wounds of Adam.
The Apostle had asked rhetorically in Romans 9 about what if there are those whom God created to display His wrath, and offers Pharoah as an example. I don’t, however, like the Reformed, regard this as evidence that anyone is predestined for perdition.
Rather the Apostle is establishing the troubling problem he observes: He feels anguish seeing how many of his fellow Jews reject the Gospel, even though he clearly rejoices in that the Gentiles are receiving it in record numbers. Paul understands here that simply being a son of Abraham according to the flesh isn’t the point (and it never was the point), it was always about faith. So the Apostle can say in Romans 9
For not all who are descended from Israel belong to Israel, and not all are children of Abraham because they are his offspring, but ‘Through Isaac shall your offspring 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 counted as offspring.
That is, what matters is faith. And further, since it’s not about blood but instead is about faith. Then the fact that Gentiles are coming to faith shows that they are, indeed, true children of Abraham.
As an aside, this is hardly a crazy idea that Paul has here, after all, throughout the Old Testament we encounter many who are not Jews but Gentiles included in God’s Covenant and promises. Consider Rahab and Ruth.
So the Apostle, in this way, considers it entirely within reason that there may be those who, because of their stubbornness of heart would become vessels of wrath in order to magnify His mercy–hence the example of Pharoah. Pharoah’s obstinate refusal to let the Hebrews go leading to his own destruction, also served to showcase the depth and magnitude of His mercy toward the Hebrews as they were brought and delivered out from Egypt, to be brought into the land of promise. The Apostle seems to be indicating that God permits the hardening of the hearts of his own people in order that, through the grace being shown in and through the Gentiles, it might become a great marvel (which the Apostle later speaks of as perhaps a means to provoke jealousy).
By the time we get to Romans 11, then, the Apostle is working through these complex ideas, and recognizes that even though the animosity toward the Gospel by many of his kinsmen is a problem, nevertheless the Gospel is being proclaimed among the Gentiles, and they are coming to the God of Abraham, Isaac, and Jacob. So even as natural branches have been pruned away, so wild branches have been grafted on.
But in all this the Apostle looks at everything with eyes of hope, that ultimately “all Israel shall be saved”, the Apostle knows the word and stories of the Prophets, he knows the Scriptures, how Israel time and again turned her back on God, and even as God brought judgment, it was to bring His people to a place of repentance, so that they might again know Him. So, too, the Apostle probably sees the situation he was living in: the rejection of the Gospel was again another example of Israel’s hard-heartedness, but as so many times before, God intended to use it as a way to show forth His mercy. As St. Paul arrives at the statement that God consigned all to disobedience “in order that He might have mercy on all” (Romans 11:32).
So the lessons of Romans 11 are that God’s covenantal faithfulness has never waned, He is not a God who abandons, but who saves. The unfaithfulness of some Israelites and God’s faithfulness toward Israel, the inclusion of the Gentiles into God’s family (Israel) through faith in Jesus does not mean the rejection of the Jews from God’s family–for what mattered was what always mattered: Faith. Unfaithful people place themselves outside of God’s house, natural branches can be cut off, wild branches can be grafted on; likewise natural branches can be re-grafted, and wild branches that are diseased and unfruitful can be cut off.
It’s not being Jewish or being Gentile that matters–but faith.
It’s not biological descent, but faith.
The mercy of God extends down through history, inviting and calling all people to repentance, bringing all who believe into God’s house. And from start to finish, Jesus Christ is what it’s all about.
Romans 11, then, is about the enduring covenant faithfulness of the God who, from the beginning, intended to meet us in Jesus Christ, who suffered and died for us and the whole world. Because it has always been God’s purpose to redeem and reclaim what He had made, not letting any be abandoned to the curse of sin and death.