You seem to be quoting a Mr. Cox with approval and he said:
Jesus taught, in John 10:16, that there was one fold and one shepherd. Paul, the great theologian, certainly knew nothing of God's having two bodies. Let Paul speak: "For he is our peace, who made both one, and brake down the middle wall of partition, having abolished in his flesh the enmity, even the law of commandments contained in ordinances; that he might create in himself of the two one new man, so making peace; and might reconcile them both in one body unto God through the cross, having slain the enmity thereby" (Eph. 22:14-16)
Paul says here that God took two men (peoples) and created one man (people) from these two. Nor does the apostle teach that God had two peoples even before this. Rather, he teaches that God took Israel (who were his people) and added the Gentiles to them -- grafted the Gentiles, who up to that time had not been God's people -- into the same olive tree. The prophet Hosea had predicted that those who were not God's people should be called his people. This prophecy was fulfilled when the Gentiles were grafted as a wild shoot into the original olive tree of God (Israel).
Just what difference does it make whether one believes God has two peoples rather than one? Many have asked if this is not a minute theological point. The importance of this premise grows in magnitude as one studies the dispensational ramifications growing out of it. The New Testament teaches us that the church is the very apex in Christ's redemptive work and that Calvary was its purchase price. An example of this teaching is Ephesians 1:22,23: "And he put all things in subjection under his feet, and gave him to be head over all things to the church, which is his body, the fullness of him that filleth all in all." Whereas the Bible calls the church the very body of Christ and the very fullness of God, the dispensationalist teaches that the church is doomed to failure, that it is a temporary instrument, and that national Israel will have a far greater ministry, following the removal of the Holy Spirit, than the church will have under the guidance of the Holy Spirit. Is this a minor point?
This quotation and every statement you and Mr. Cox have made about the "middle wall of partition" seems to apply that phrase to redemption alone.
The new public institution the church is not a universal invisible mystical body but a local visible body of water baptized believers. Indeed, the words "the house of God" is found only 88 times in Scripture and 1 Tim. 3:15 is the 86th time it occurs and in every single solitary previous instance it is descriptive of the institutional public house of worship where a qualified ministry administer qualified ordinances and that is precisely the context of 1 Tim. 3:1-3.
I believe that salvation, the gospel, the Savior have been the same since the Garden of Eden until Revelation 22. Prior to Isael God had an elect people. Israel as a nation was and still is God's elect nation, but not all ethnic Jews constitute that spiritual ethnic elect Israel. However, God as in all cases of election will save that nation at a point in time in the future (Rom. 11:25-28) completing His promise to Abraham of an elect nation from his own physical loins as he will also complete His promise to Abraham about an elect people from all nations. Romans 11:1-32 is designed to assure that God's election of Israel to Salvation is not God's election among the Gentiles. Church does not equal Israel any time in history, but rather the new institutional house of God built by Christ in his own earthly ministry provides EQUALITY of worship and status of Jews and Gentiles elect together, without minimizing or denying God's future election of ethnic Israel as a nation to salvation.