In the first eleven chapters of Romans, Paul catalogs the mercies of God in God’s provision of righteousness through the gospel. First, in Romans 1:1—3:20 Paul considers the universal human need for God’s righteousness, as all are unrighteous and separated from God. Then in Romans 3:21—4:25 Paul lays out how God applied righteousness through faith to all who believe in Jesus, outlining three different and significant types of descendants of Abraham: 1) ethnic Israel (Romans 4:1), 2) believing Gentiles (Romans 4:11), and 3) believing Jews (Romans 4:12). These three sets of descendants of Abraham are especially important for understanding the partial hardening and the fullness of the Gentiles that Paul talks about in Romans 11.
Romans 5—8 discusses the implications of that righteousness applied in freeing believers from the penalty and bondage of sin (Romans 5—7) and assuring them of a present and future of reconciliation and peace with God (Romans 8). At the end of Romans 8 is a powerful affirmation of the believer’s eternal security—God will keep His promises to those who have believed in Jesus Christ, and they will never be separated from the love of Christ (Romans 8:35).
While discussing these mercies of God, Paul seems to anticipate that his readers might wonder why, if God is so faithful to restore those who believe in Jesus, God’s promises of restoration to Israel do not seem to be fulfilled yet. Simply put, if God is faithful, and if His promises to believers are trustworthy, then why is He not keeping His promises to Israel? It is to answer this concern that Paul writes Romans 9—11, as he introduces the ideas of a partial hardening of Israel and the fullness of the Gentiles (Romans 11:25).
In Romans 9 Paul expresses his love for his Jewish brethren (Romans 9:1–5) and recognizes that the covenant promises are to be fulfilled to a specific group of Abraham’s descendants. Paul shows the distinct groups by highlighting God’s choosing of Abraham, Isaac, and Jacob and affirms that God’s blessing would be for those descendants who believe in the Messiah (Romans 9:33). Salvation would not only be for believing Jews, though, as Gentiles could also call upon the name of the Lord for salvation (Romans 10:12–13). While there are believing Jews and Gentiles, Paul explains that the nation of Israel as a whole has not yet received her Messiah (Romans 10:18—11:10), but they will one day be saved through believing in their Messiah (Romans 11:26).
In the meantime, Paul explains that there is a partial hardening of the nation—that many will refuse the Messiah—until the fullness of the Gentiles occurs. Israel’s hardening will continue until the divinely set number of Gentiles are saved: “Some of the people of Israel have hard hearts, but this will last only until the full number of Gentiles comes to Christ” (Romans 11:25, NLT).
Paul recognized that Israel’s failure to accept the Messiah when He came offering the kingdom represented blessing for the Gentiles because, instead of setting up that kingdom on earth at that time, Christ died to pay for the sins of all. In so doing, Christ fulfilled the promise God made to Abraham that in Abraham’s seed all the peoples of the earth will be blessed (Genesis 12:3b). That partial hardening of Israel also represented a shift in focus to the announcement of salvation to the Gentiles. Paul acknowledged himself as an apostle to the Gentiles (Romans 11:13) and sought that many Gentiles would come to know Christ so those promises could be fulfilled and then the Jewish people might return to their Messiah (Romans 11:14–15). Paul alluded to this in 2 Timothy 4:17 when he expressed gratitude for God’s sustaining him so that Paul might fulfill his ministry and that all the Gentiles might hear.
Even though God’s promises to save the nation of Israel are not presently being fulfilled, Paul recognizes that God will keep those promises after the fullness of the Gentiles. Paul seems to be building on the foundation of Daniel 9, in which is revealed a 490-year prophetic timeline after which God will accomplish His covenant blessings for Israel. After the first 483 years of the timeline, the Messiah was cut off (Daniel 9:26a), signaling a shift in the focus away from Israel as Gentiles (Rome) would dominate, and there would be wars and desolation. But one day in the future, the ruler who would be known as the Antichrist would make a seven-year agreement with Israel. That last seven years of the timeline would begin to return the focus back to Israel and would conclude the times of the Gentiles of which Jesus spoke in Luke 21:24.
The fullness of the Gentiles in Romans 11:25 reminds us of God’s global focus (with the universal proclamation of the gospel of salvation) and chronology (with the times of the Gentiles not yet complete). One day, the fullness of the Gentiles will be complete, and God will deliver the nation of Israel. Anyone who might have doubts about God’s faithfulness in keeping His promises can consider these passages as important reminders that God has a detailed plan that He is fulfilling patiently and carefully.