The Idea in Brief
The New Covenant is the Gospel promised by the Prophets of the Hebrew Bible. What is different in the current age is that this New Covenant fuses (or baptizes) converts into the mystical Body of the Christ. That is, the blood of Jesus Christ is the New Covenant (Luke 22:20). In this respect, the New Covenant promised in the Hebrew Bible is not an extension of the Old Covenant but of both the Davidic Covenant and the Abrahamic Covenant, by which the "nations of the world were to be blessed through the seed of Abraham" (Gen 18:18; Gen 22:18; and Gen 26:4). So the twist is that in the current age, the New Covenant is available to everyone, Jew and Gentile.
Discussion
Background
The New Covenant mentioned in the Prophets of the Hebrew Bible was about the placement and writing of the Laws of the Lord on the mind and heart, respectively (Jer 31:33); the indwelling presence of the Spirit of the Lord (Ez 11:19-21 and Joel 2:28-29) whose power will enable continued and faithful obedience (Ez 36:25-27); the re-gathering of all Israelites into the Promised Land (Jer 16:15 and Ez 34:13-16), which will include resurrection from the dead (Ez 37:12); the forgiveness of sins (Jer 31:34); and the universal knowledge of the Lord throughout the earth (Hab 2:14; Is 11:9; Jer 31:34). Finally, the removal of the curse from the ground appears to be another aspect of the New Covenant (Hosea 2:18, Is 11:6-9 and Ez 34:23).
The Apostle Paul indicates in Ephesians 2:11-22 that Gentiles have access to this New Covenant through the blood of Christ.
Ephesians 2:12-13 (NASB)
12 remember that you were at that time separate from Christ, excluded from the commonwealth of Israel, and strangers to the covenants of promise, having no hope and without God in the world. 13 But now in Christ Jesus you who formerly were far off have been brought near by the blood of Christ.
The "blood of Christ" is the New Covenant (Luke 22:20), so we know that Paul is talking about the New Covenant, for which the Gentiles are no longer excluded. That is, at the beginning, the faithful Jewish remnant at Pentecost, comprised of the disciples of Jesus, had received the New Covenant from heaven. (The day of Pentecost was the same day that the nation of Israel at Sinai had received the Old Covenant from heaven through Moses.) Subsequent to Pentecost, the New Covenant was then extended to non-Jews through fusion (baptism) into the mystical Body of Christ -- Cornelius and his household were the first in this regard (Acts 9-11). So non-Jews participate in the Jewish promises through union or "grafting" (Romans 11:17-24) into the mystical Body of Christ.
Some graphs will help to explain, which are only conceptual for the purposes of illustration. First, this graph (please click here) portrays the arrangement of the Old Covenant in the Hebrew Bible. (Please note that there is ALWAYS a faithful remnant of believers somewhere; for example, please see 1 Kings 19:18.) According to the Christian New Testament, when the nation of Israel had rejected its king (Jesus called the Christ), the faithful Jewish remnant remained and became the Jewish cadre to receive the New Covenant at Pentecost. Please click here.
The Relationship between Jews and Gentiles in the New Covenant
Please click here, and please note how the promise in the Book of Genesis regarding the Seed of Abraham (and also David) was to bless the world. At the current time, the appearance of Gentiles into the New Covenant occurs through Jesus Christ, whose blood as already noted is the New Covenant (Luke 22:20). Thus Jews and Gentiles become one as the following verse indicates -
Colossians 3:10-11 (NASB)
10 and have put on the new self who is being renewed to a true knowledge according to the image of the One who created him— 11 a renewal in which there is no distinction between Greek and Jew, circumcised and uncircumcised, barbarian, Scythian, slave and freeman, but Christ is all, and in all.
In this respect, the definition of Jew in the Christian New Testament is not "one who is circumcised with hands" but one whose "circumcision is of the heart" (Col 2:11). For such a person the "Promised Land" is centered in the citizenship of heaven (Phil 3:20), the place of the "Jerusalem above" (Gal 4:26), which is also called the "Zion above, the heavenly Jerusalem" (Heb 12:22).
One may ask why the Hebrew Bible points to the exclusive promise of the New Covenant for Israelites (that is, the biological descendants of Abraham and proselytes, who are ethnic Jews). Even the New Testament reiterates this exclusivity of the New Covenant with "the House of Israel and the House of Judah" (Hebrews 8:8). The answer is that the narrative of the Christian New Testament indicates that the Gentiles were "grafted" as wild olive branches into the root, who is Jesus Christ (Rom 11:11-24). This "grafting" was the so-called mystery revealed to the Apostle Paul.
In several passages of the Christian New Testament the Apostle Paul speaks about the mystery, concerning which he had received direct and special revelation from heaven. The verses here indicate that this mystery was not revealed in the Hebrew Bible; that is, the New Covenant would unite Jews and Gentiles into "one" body, and therefore establish peace between Gentiles and Jews through mystical union into the Body of Christ (Eph 2:13-16).
Paul also indicated that the inclusion of Gentiles into the Body of Christ would continue until the "fullness of the Gentiles" was complete.
Romans 11:25-27 (NASB)
25 For I do not want you, brethren, to be uninformed of this mystery—so that you will not be wise in your own estimation—that a partial hardening has happened to Israel until the fullness of the Gentiles has come in; 26 and so all Israel will be saved; just as it is written,
“The Deliverer will come from Zion,
He will remove ungodliness from Jacob.”
27 “This is My covenant with them,
When I take away their sins.”
Based on my own limited understanding of the Hebrew Bible (both language and narrative), the graph depiction here portrays the general eschatological outlook from the perspective of the Hebrew Bible, which the Apostle Peter had assumed at the time of Pentecost. That is, the Apostle Peter had expected the imminent Day of the Lord (Acts 2:17-20), when the Messiah would come and save ("Hosanna" = save us) the people of Israel from Gentile world power. (According to Acts 1:6, there was imminent expectation of the establishment of the visible theocratic kingdom on earth.) Not surprisingly, in the same chapter of Acts, the Jewish believers at that time and at that place divested themselves of all their worldly possessions (Acts 2:43-47). The appearance of Gentiles into Christianity then came by complete surprise (Acts 9-11), for which Jewish believers were caught unawares (Acts 11:1-3).
In Galatians 2:1-2, the Apostle Paul appears to have disclosed this mystery to the Jewish believers in Jerusalem sometime after Paul's first missionary journey. After the Apostle Paul disclosed the mystery, the graph depiction here portrays the eschatological expectation understood in light of the mystery -- that is, in concert with the Book of Revelation, the mystery appears to be an "intercalation" of time splitting the "70 Weeks" of Daniel. In this regard, the Day of the Lord does not appear to have occurred during the First Century, since Gentile Christians (non-Jews) living in Thessalonica (mainland Greece) were worried the Day of the Lord had begun (2 Thess 2:2). In other words, the Day of the Lord is a time when the not only Israel will be affected, but also the entire world (to include places like mainland Greece), and such is the general genre of the Book of Revelation.
In summary, the New Covenant is in partial fulfillment at the current time and includes Gentiles, but only through direct fusion, or union into the mystical Body of Christ. After an unknown point of time, the "wild olive branch" will be broken off (Rom 11:22) because the "Fullness of the Times of the Gentiles" will be completed, and the original olive branch will continue and proclaim the New Covenant during the Day of the Lord (i.e., the last "week" of Daniel's 70 weeks).
What is the Eschatological Outlook for Jews and Israel?
The Apostle Paul is very clear about his reaffirmation of Israel, which had received the gifts and promises of the Lord in the Hebrew Bible.
Romans 11:25-28 (NASB)
25 For I do not want you, brethren, to be uninformed of this mystery —so that you will not be wise in your own estimation— that a partial hardening has happened to Israel until the fullness of the Gentiles has come in; 26 and so all Israel will be saved; just as it is written,
“The Deliverer will come from Zion,
He will remove ungodliness from Jacob.”
27 “This is My covenant with them,
When I take away their sins.”
28 From the standpoint of the gospel they are enemies for your sake, but from the standpoint of God’s choice they are beloved for the sake of the fathers; 29 for the gifts and the calling of God are irrevocable. (emphasis added)
The Book of Acts in addition to various other New Testament epistles (to include many written by Paul) indicate that many Jews in the First Century rejected Jesus as the Christ. However, this "hardening of heart" was "partial" because some Jews (such as Paul) became converts to Christianity so not all Jews rejected Jesus as the Christ -- these Jews appear in Galatians 6:16 to be the "Israel of God" (Faithful Israeli Remnant during the mystery era). Notwithstanding that many Jews oppose Christianity (in the sense of rejecting Jesus as their Messiah), this opposition never can nullify the gifts and promises made to Israel through the lens and perspective of the Christian New Testament. Thus the mystery is only temporary until such time as the "Fullness of the Gentiles" occurs, and Israel continues the eschatological trajectory (Day of the Lord) as was understood by Peter when the New Covenant began.
Conclusion
In summary, the New Covenant forged with Israel will receive its complete fulfillemnt in the future. This fulfillment will include the placement and writing of the Laws of the Lord on the mind and heart, respectively (Jer 31:33); the indwelling presence of the Spirit of the Lord (Ez 11:19-21 and Joel 2:28-29) whose power will enable continued and faithful obedience (Ez 36:25-27); the re-gathering of all Israelites into the Promised Land (Jer 16:15 and Ez 34:13-16), which will include resurrection from the dead (Ez 37:12); the forgiveness of sins (Jer 31:34); and the universal knowledge of the Lord throughout the earth (Hab 2:14; Is 11:9; Jer 31:34). Finally, the removal of the curse from the ground appears to be another aspect of the New Covenant (Hosea 2:18, Is 11:6-9 and Ez 34:23).
The current time however in the current era is only an intercalation of time, in which Gentiles and Jews have joint access to partial fulfillment of the New Covenant through direct fusion, or union, with the mystical Body of Christ. This union was not revealed in the Hebrew Bible, and therefore appears as the mystery within the Christian New Testament.
For the conclusion of this discussion of the New Covenant, please see this post.