Here is a quote from Pastor Conrad Imbewe, it is Voddie Baucham's teaching on the matter, see the original posting here. http://www.conradmbewe.com/2011/08/4th-day-at-zambian-annual-reformed.html
Secondly, if you suffer from a spiritual inferiority complex then you make light what God has done for them—i.e. the Jews (v.14-18). The Jews also needed to be saved (see Romans 2:17ff). What they had in their ethnicity, culture, and religion was not enough. Their problem was a sin problem and so they needed the blood of Christ to save them.
Thirdly, if you suffer from a spiritual inferiority complex then you are accusing God of using some inferior materials in building his church (see v.19-22). Paul here uses construction language. That which is being built is a holy temple. As with any painting, the excellence of the painter is what dignifies materials that he uses. Remember, that the builder is God himself. Thus a chief will sit next to a slave and worship the Lord singing, “In the cross, in the cross, be my glory ever…” This will be even more evident when we are all gathered with the Saviour in eternity. At that point what will matter will not be ethnicity but only the cross. This is what the cross-centred life is all about.
As we streamed out of the Lusaka Baptist Church auditorium, it was evident that skin colour, ethnicity, nationality were overshadowed by the power of the cross. Yes, we had come from different tribes and nations across the world but we were all one in Christ. We went home at the end of the day sensing once again that God has been good to us."