Ephesians 3:6 KJV
That the Gentiles should be fellowheirs, and of the same body, and partakers of his promise in Christ by the gospel:
Scofield's Notes says,
"That the Gentiles were to be saved was no mystery (Rom_9:24-33); (Rom_10:19-21). The mystery, "hid in God", was the divine purpose to make of Jew and Gentile a wholly new thing - "the church, ....[I removed this segment because of its universal church doctrine].... (1Co_12:12); (1Co_12:13), and in which the earthly distinction of Jew and Gentile disappears; (Eph_2:14); (Eph_2:15); (Col_3:10); (Col_3:11). The revelation of this mystery, which was foretold, but not explained, by Christ (Mat_16:18) was committed to Paul. In his writings alone, we find the doctrine, position, walk, and destiny of the church."
The first half of the book of Ephesians is taken up with this doctrine of unity among believers in a local church. The modern practice of having a church for every nationality is completely unbiblical and tends toward a universal church mentality; "Since we belong to the 'true church' we need not concern ourselves with working out the mystery of fellowship in a local congregation of diverse believers." We need to return our churches to a "melting pot" mentality where everyone is welcome because in the Lord we are "a whole new thing."