Internal division has threatened the church from its earliest days. Ethnic divisions between Jews and Gentiles threatened to perpetuate segregation in Ephesus. Fights over spiritual gifts fractured the Corinthians. While each church had different obstacles to solidarity, Paul prescribes the same remedy to both: teaching on the Trinity.
The unity of the Godhead is essential to Paul’s argument about the church. First, it’s necessary to understand that there’s only one God and only one church—this forces us to see the equality of all Christians. We must not elevate any one ethnicity nor a particular spiritual gift above others.
To the Ephesians, he buttresses his argument about church unity with two Trinitarian statements:
For through him [Christ] we both [Jews and Gentiles] have access in one Spirit to the Father. Eph 2:18
In him [Christ] you also are being built together into a dwelling place for God by the Spirit. Eph 2:22
After unveiling the “mystery” of the church where Jew and Gentile are united in Christ (chapter 3), he reminds them of their shared bond in the Trinity:
There is one body and one Spirit—just as you were called to the one hope that belongs to your call—one Lord, one faith, one baptism, one God and Father of all, who is over all and through all and in all. Eph 4:4–6
As for the Corinthians, their elevation of certain gifts demeaned the common source of each gift: the Trinity.
Now there are varieties of gifts, but the same Spirit; and there are varieties of service, but the same Lord; and there are varieties of activities, but it is the same God who empowers them all in everyone. 1 Cor 12:4–6
To drive home this unity, Paul says:
For just as the body is one and has many members, and all the members of the body, though many, are one body, so it is with Christ. For in one Spirit we were all baptized into one body—Jews or Greeks, slaves or free—and all were made to drink of one Spirit. 1 Cor 12:12–13
The Spirit not only brings us into union with Christ, but unifies everyone in the church into the same body. The one church, to which all Christians belong regardless of ethnicity, and the one God who empowers all Christians in spiritual service compels believers to be “eager to maintain the unity of the Spirit in the bond of peace” (Eph 4:3).