"There is one body and one Spirit, just as also you were called in one hope of your calling; 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)."
After describing the attitudes necessary for oneness in Ephesians 4:1-3, Paul describes the theological basis for it in a nutshell. Although he already gave an exposition for the basis of unity in the first three chapters, he reminds his readers once again that unity is not only man-made, but God-made. To not preserve the unity of the Spirit in the bond of peace is to put asunder what God joined into one (Eph 2).
One of the interesting things about this list is there are seven items. Since the number seven symbolically denotes perfection, it is likely that this numbering is intentional. It communicates that when we come to terms with all of these, we are a unified church, hence a complete and mature church.
There is one body. This, of course, is referring to all faithful believers. In order for the body to be effective, each part has to work with each other. We are all equally heirs (Gal 3:28), and have the same care for one another (1 Cor 12:25). That is biblical egalitarianism.
There is one Spirit. If we fight and quarrel, if we work against instead of for each other, then we are following our individual "spirit" rather than the one Spirit. The Spirit gives various gifts for the purpose of building up the body together. Paul will develop this idea further in this chapter.
There is one hope of our calling. This is talking about our goal and expectation. If there is no oneness in the body, then maybe the focus is all wrong. We are united by the fact that we all are working toward the same goal and are helping each other to reach that goal.
There is one Lord. This is talking about our Lord Jesus. When we have a common Lord and master, then we will be able to work together since he is the focus of what we do. Neither our desires, hobbies, or pet peeves are what drives us. Our common desire to please the same Lord bring us all together.
There is one faith. There is only one way to God, which is Jesus himself (John 14:6). The object of our faith is Jesus Christ. If the prince of peace is our focus, then we can preserve the unity of the spirit in the bond of peace.
There is one baptism. Only baptism into the Father, Son, and the Holy Spirit brings us together as God's family (Matt 28:18-20). It is interesting that all three are mentioned here.
There is one God and Father of all who is over all and through all and in all. If we are truly in tune with God, he will permeate all we do. It is hard to be disagreeable, factious, and selfish when you truly realize that it is God who is between, in, and through us.
So far, this chapter in Ephesians has shown that preserving unity has both a theological (v.4-6) and attitudinal (v.1-3) basis. When the body works together as a unit, then it can truly serve others. It can demonstrate love. It can be a strong witness to the Gospel.