Ephesians 1:7-10
In him we have redemption through his blood, the forgiveness of our trespasses, according to the riches of his grace, which he lavished upon us, in all wisdom and insight making known to us the mystery of his will, according to his purpose, which he set forth in Christ as a plan for the fullness of time, to unite all things in him, things in heaven and things on earth.
Sinclair Ferguson says that B.B. Warfield might be the greatest theological mind American has ever produced. One of the great contributions Warfield made was what he called the basic theological principle of the unity of humanity. That is, there was only one Adam and Eve, and from Adam and Eve came the whole human race. There were actually various theories in Warfield's day that there were different origins of humanity. Even after the population accepted that humanity was one class of humans, they did argue that there were various classes or qualities of humanity. We're always capable of disparaging another race. He said that unity of humanity was unbroken from creation to the flood, but Babel was where the differentiation of ethnicities occurred out of rebellion against God. He said, "what God had joined together, men themselves, in rebellion, pulled asunder."
Another principle we find in scripture that Warfield made much of was the definition of the mystery of the gospel. Ephesians 3:6 says, "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." So Paul argues that because humanity is one, therefore all of humanity has sinned, and all of humanity is therefore in desperate need of redemption. And that redemption comes through one man, Jesus Christ. Then he goes on to say that Christ makes one new humanity (Ephesians 2:15). Gentiles and Jews are not two classes but one new people who will call each other father and mother, sister and brother, and worship together as equals in the Church of Jesus Christ.
Pursuing this unity, Warfield said, was basal in Paul's ministry. Paul explicitly mentions that ministry of reconciling Gentile and Jew in nine of his thirteen epistles. He saw it as the reason he was being kept alive – to preach the gospel of reconciliation. It had an apologetic purpose to it. He was effectively asking, "how could anyone believe that a holy God could be reconciled to sinful people if they don't see objectively demonstrated in the church the reconciliation of people who were thought previously to be irreconcilable?" If Gentile and Jew are not reconciling, worshipping together, and serving one another, how is anyone to take it seriously that God can reconcile with unholy people?
Francis Schaffer put it this way in his book The Mark of Christianity, "Jesus gave the world permission to dismiss us if it did not see us loving one another." Paul might say that the world has permission to dismiss us if it doesn't see us reconciling with one another. The unity of the human race, Warfield said, is the basis of the demand to recognize the dignity of all humanity and the entire scheme of restoration. It's a mandate, it seems to me, to unite visibly in worship.