We are part of a congregation that ministers through four languages, directly or indirectly – actually 5 if you count Mandarin and Cantonese as two languages. So unity is something we talk about. So it is interesting to read about the conflict between Paul and Peter in the multi-cultural church in Antioch.
Peter, who had brought in the first Gentile converts (see Acts 10) was first enjoying a fine church supper and close friendship with gentile believers in Antioch, until some nay sayers appeared. Then he separated – we presume in order not to divide the church or not to put a stumbling block in front of a Jewish audience.
Paul would not let this stand – because it was not only a breach of unity, it was a denial of the Gospel, and specifically a denial of the concept of justification.
It is not clear if verses 17 through 21 were part of the Paul to Peter speech, or Paul’s explanatory aside to the Galatians. In any case, Justification by faith is the basis of unity; conversely division is a denial of that gospel.
We ourselves are Jews by birth and not Gentile sinners;  yet we know that a person is not justified by works of the law but through faith in Jesus Christ, so we also have believed in Christ Jesus, in order to be justified by faith in Christ and not by works of the law, because by works of the law no one will be justified.
 But if, in our endeavor to be justified in Christ, we too were found to be sinners, is Christ then a servant of sin? Certainly not!  For if I rebuild what I tore down, I prove myself to be a transgressor.  For through the law I died to the law, so that I might live to God. I have been crucified with Christ.  It is no longer I who live, but Christ who lives in me. And the life I now live in the flesh I live by faith in the Son of God, who loved me and gave himself for me.  I do not nullify the grace of God, for if justification were through the law, then Christ died for no purpose.
We have never heard a sermon that ties multicultural unity to the doctrine of Justification. We have heard that it is too much to ask for people to overcome their prejudices and divisions in order to appreciate the work of Christ.