Before I get into the OT prophecies which are quoted by the Apostle Paul in Romans 15:9-12, it is important to examine the opening phrases that he uses just before quoting the OT scriptures. Here is the text from ESV:
For I tell you that Christ became a servant to the circumcised to show God’s truthfulness, in order to confirm the promises given to the patriarchs, and in order that the Gentiles might glorify God for his mercy.
This scripture, which is given great importance by practically nobody, shows us the nature of Christ’s ministry among the children of Israel. You can go back and read it for yourself in the gospels. Jesus came to the nation of Israel. His ministry was within the nation of Israel. His miracles were to Israelites. His teaching, preaching, and parables were to Israelites. He sent His Israelite disciples out to the lost sheep of Israel, and promised his disciples that they would sit on twelve thrones judging the twelve tribes of Israel. He instituted the New Covenant with Israel in His own blood. He was crucified just outside Jerusalem, the Israelite city.
Note that the phrase used here is "the circumcised". To do an exhaustive study on this one term would be space prohibitive. How about a summary? Circumcision was a sign given to Abraham as a token of his faith in the promises that he had already believed in. Abraham believed the promises while he was uncircumcised and received the righteousness of God at that time. Later, he was circumcised, but that did not make him righteous. It was his faith that made him righteous.
Part of the Abrahamic Covenant included all males of Abraham’s offspring to be circumcised on the eighth day, Genesis 17:10. This was later reinforced when God spoke from the tabernacle in Leviticus 12:3. But a greater focus was placed on the circumcision of the heart in Deuteronomy 10:16 as a present commandment, and in Deuteronomy 30:6 as a future promise which God would fulfill corporately to the nation of Israel.
So when Paul states that Messiah became a servant to the circumcised, the plain meaning we would assume is that He became a servant of the nation of Israel, but more specifically, those believing Israelites who had been obedient not just to the physical law, but to the spiritual law and had circumcised their hearts. For them, (those believing Israelites), Messiah was willing to serve, suffer, and die. So Messiah came to the entire nation of Israel, but more specifically to the elect of Israel.
Before moving on, Abraham received the promise, believed the promised, and obtained righteousness with God before receiving circumcision, showing that it was not necessary to obtain righteousness with God. God laid it out this way so that anyone, anywhere, from any nation could believe in God’s promises without having to go through any ritual to have a right standing with God. Romans 4:11-12 tells us that this occurred that Abraham might be the father of ALL who believe even if they have not been circumcised. Even if someone is a pagan, knowing nothing of the laws of the God of Israel, they can believe in the promises laid out therein, and receive a righteous standing with God based on their faith. This actually makes Abraham the father of MANY nations, not just the nation of Israel.
Now let’s pay a little attention to the next phrases. The reason that Messiah came to the circumcised is to confirm the promises made to the patriarchs (insert Abrahamic Covenant here) and further, that the Gentiles might glorify God for His mercy. So there can be no "great melting pot" of Gentiles becoming Israelites as they become one in Messiah. Gentiles who believe in the Messiah of Israel maintain their ethnicity, but are full participants in the righteousness which God gives to those who believe in Messiah as Savior which makes Abraham the father of many nations. God intends to fulfill the promises made to the patriarchs through Israel [still as an ethnic people.] Gentiles (non-Israelites) will also glorify God for His great mercy as those promises to Israel are brought to pass.
The present fulfillment of Gentiles glorifying God is manifested in the church. Israelites and Gentiles both are glorifying God for His faithfulness to the nation of Israel. Both have equal status in Messiah since they both possess the righteousness of Messiah. The future fulfillment of Gentiles glorifying God will be manifested as Israel is regathered, restored, and raised up to a place of prominence among the Gentile nations. Gentile nations will be glad that Israel has a preeminence matched by none in the world, and it will be due to Israel’s king being second to none. These truths will be fleshed out in greater detail as we examine which OT scriptures Paul sees as being fulfilled to Gentiles in Messiah.
Summing up, Jesus the Messiah came to the nation of Israel, and more specifically, those within the nation of Israel who are truly His people. He did this to fulfill promises (covenants) made to Abraham and other patriarchs. One of these promises was that all nations (Gentiles) would glorify God for His mercy noted in several places in the OT which Paul will now quote with very little explanation. He left that for us to study.
Have fun and stay busy – Luke 19:13
-The Orange Mailman