The following is a footnote that is taken from a research paper on Acts 1:6-8 that I am currently working on:
A brief excursus on my understanding of kingdom restoration as it relates to the people of God in previous times and today:
In Matt. 21:43, Jesus teaches that the kingdom was going to be taken away from Israel and “given to a people producing its fruits.” The word “people” here is ἔθνος, the same word translated “nation” in Rom. 10:19 and 1 Pet. 2:9. In Rom. 10:19, the word refers to the people whom the Lord has turned to and poured out His blessings upon (i.e., the Gentiles), thereby making unbelieving Jews “jealous.” Considering the likely context of Peter’s first epistle, in 1 Pet. 2:9 we can surmise that his usage of ἔθνος refers to both Jewish and Gentile believers in the Church. It is this “nation” or “people” who have received the first blessings of the kingdom restoration that was inaugurated by Christ in the new covenant age that were poured out, at least in its initial stages, at Pentecost.
This does not mean that God has rejected His former people Israel (Rom. 11:1), for they may participate in this kingdom restoration via the new birth by the Spirit; they are not summarily excluded from it. There remains a number of Israelites (like Paul) who participate in the kingdom as part of the elect “remnant [of Jews], chosen by grace” through faith in Christ (Rom. 11:5).
The rest of unbelieving Israel has become “hardened,” and are thus excluded from the promise of kingdom restoration and the entering of God’s rest due to their lack of faith (Rom. 11:7, 25; Heb. 3:11-12; 3:18-4:1). Hardening is a form of divine punishment and retribution for sin. Israel was “broken off,” (Rom. 11:17) they were not “spared” (Rom. 11:21). These are graphic word pictures that are intended to display the wrath of God toward sinners that are hostile to His nature, character, and saving intent. When given their full weight, they are pictures of severity that do not appear to leave any hermeneutical wiggle room for some type of future salvation. This is a graphic picture of God reacting in the strongest possible way against the sin of those who have rejected His dear Son (Leon Morris, The Apostolic Preaching of the Cross, third edition [Grand Rapids: Eerdmans, 1965], 224). This hardening of a portion of unbelieving Jews will continue until this age is brought to a close by the return of the King. In this age, kingdom blessings fall upon all (Jew and Gentile alike) who are grafted into the one olive tree of believers of all ages (Rom. 11:17-24).
That Gentiles would become fellow heirs with Jews in the kingdom blessings of God by faith (Eph. 3:6; Gal. 3:7-9, 28-29; cf. 2 Cor. 1:20) is the revelation of the truth of God that was veiled in previous times (μυστήριον, “mystery” in Rom. 11:25). Hence, “all Israel” (Rom. 11:26) refers to all of the people of God throughout all of the ages of salvation history: all the OT saints plus the elect remnant of Israelites who have faith in Christ in the present new covenant age plus all Gentile believers.
Such a reading of “all Israel” is natural in the light of the fact that Gentile believers are depicted as being grafted into the one “olive tree” of God (Rom. 11:17-24), a term that was used in the OT as a name and picture of believing Israel (Jer. 11:16; cf. Ps. 52:8). Thus, “all Israel” = “the olive tree” (with Jewish and Gentile branches) = the unified people of God of all ages. (Cf. “Israel of God” as a referent to the church in Gal. 6:16 and “Israel” as referring to the Messiah in Isa. 49:3 for other instances of divinely inspired flexibility regarding the employment of the term “Israel.” Thus, seeing the referent of “Israel” in Rom. 11:26 as referring to all true believers of all ages does not stretch this term beyond understanding.)
At the present, unbelieving ethnic Israelites are “enemies of God” while believing Israelites (like Paul) “are beloved for the sake of their forefathers” (Rom. 11:28). Gentiles have received “mercy” in the new covenant age because of the “disobedience” of unbelieving Israelites. However, “mercy” is still being offered to those Jews who would repent and believe the gospel (Rom. 11:31). At various points in salvation history, “all” have been “disobedient,” with the divine purpose that the Lord may pour out His rich kingdom blessings “on all” (Rom. 11:32). The sheer enormity of such a plan should cause all believers to glory and revel in the majesty of our great and wonderful God (Rom. 11:33-36)!

