"When you read this, you can perceive my insight into the mystery of Christ, which was not made known to the sons of men in other generations as it has now been revealed to his holy apostles and prophets by the Spirit. This mystery is that the Gentiles are fellow heirs, members of the same body, and partakers of the promise in Christ Jesus through the gospel." (Eph 3:4-6)
The Apostle Paul in his epistles strives to make clear what the new covenant means for the people of God, he particularly deals with the new covenant relationship of the Jews with the Gentiles. In his epistle to the Ephesians he speaks of a mystery that has only after the coming of Christ been clearly revealed, and he informs us that this mystery is that the Gentiles are fellow-citizens of Israel (Eph 2:19) and are no longer aliens and strangers to the covenants and promises belonging to the people of God (Eph 2:12).
When we come to chapter 3 in Ephesians the Spirit continues to highlight this theme saying that this recently revealed mystery, that the Gentiles and Jews are "members of the same body", is based upon the fact that the promises of God to Jew and Gentile alike all share one Mediator, Jesus Christ. Or, stated bluntly, God in Christ did not choose to redeem Jews only, but men from every tribe tongue and nation. Also, God in Christ is not satisfied with ruling over a strip of land abutting the Mediteranean sea and the Jordan river, He came to rule the whole world (Eph 1:22).
There are no two distinct and separate covenant peoples, because there is One Savior, one body, one baptism, and one Spirit. In fact the first 5 verses in Eph chapter 4 seem to really be rebuking the desire on the part of some to divide the people of God, given the previous content in Ephesians regarding the inclusion of Gentiles the threat to unity probably came from those desiring to emphasize a Jewish particularism and push the Gentiles into the outer courts of the church. You see, Dispensationalist Zionism and the two people of God doctrinal error are nothing new, Paul had to rebuke it many a time. The pernicious nature of this error came to the point of the Spirit through Paul confronting another Apostle sinning by adopting the two people of God view and practicing its implications at the dinner table (Gal 2).
The marriage supper of the lamb will not have a two tiered banquet table, there will not be some kiddie table off to the side with Mac N Cheese and a cheap Wal-Mart box of wine for the Gentiles to enjoy while the Jews get the best seats, choice cuts of Kobe beef and chalices of new wine filled to the brim being constantly replenished by little cherubs fluttering about (yes, I mean the little baby ones). As silly as that description may appear it really seems to be the vision of unity between Jew and Gentiles many Dispensationalists gravitate toward. Is this biblical? Not in the least bit, rather, all are one in Christ, Pentecost should teach us this, as well as Paul's Spirit filled lesson in table manners.