One in Christ
11 Therefore remember that at one time you Gentiles in the flesh, called “the uncircumcision” by what is called the circumcision, which is made in the flesh by hands— 12 remember that you were at that time separated from Christ, alienated from the commonwealth of Israel and strangers to the covenants of promise, having no hope and without God in the world. 13 But now in Christ Jesus you who once were far off have been brought near by the blood of Christ. 14 For he himself is our peace, who has made us both one and has broken down in his flesh the dividing wall of hostility 15 by abolishing the law of commandments expressed in ordinances, that he might create in himself one new man in place of the two, so making peace, 16 and might reconcile us both to God in one body through the cross, thereby killing the hostility. 17 And he came and preached peace to you who were far off and peace to those who were near. 18 For through him we both have access in one Spirit to the Father. 19 So then you are no longer strangers and aliens, but you are fellow citizens with the saints and members of the household of God, 20 built on the foundation of the apostles and prophets, Christ Jesus himself being the cornerstone, 21 in whom the whole structure, being joined together, grows into a holy temple in the Lord. 22 In him you also are being built together into a dwelling place for God by the Spirit.
In this section, Paul wants the Gentile Christians to consider themselves to be in equal standing with the Jews before God. The old wall of hostility has been broken down by the death and resurrection of Jesus. In Him, they are one people.
Paul also brings out the fact that the Gentiles need not submit to circumcision. This rite no longer serves as the entry rite into the Old covenant. Baptism is now the entry rite for all. Baptist is the circumcision “made without hands.” Baptism is for all, Jew and Greek, slave and free, male and female.
Paul reminds the Gentiles of what they were missing out on before they believed. They had been alienated from the life of God, sojourners. They were outside of the house of God. Now they have been brought near through the blood of Christ. They are now members of God's one-way covenant established at the cross. They are partakers of the eternal joy of salvation, life, and forgiveness.
Their life now in Christ is markedly different from the life in paganism. Whereas they had been physically excluded from the worship life of Israel by an actual wall, that wall has now been removed. The Gentiles now have full access to God through Jesus. The reconciliation with God has been established. The reconciliation between Jew and Gentile has also been established.
The Universal atonement and reconciliation of all things is in view here. Again, Paul points to the cross as the point of reconciliation. There is no Gospel without this actual human body of the God-Man Jesus being crucified and dying. This benefits of his sacrifice are given out through the means of grace, Baptism, Supper, Word.
Peace is established between man and God, and man and man. (Num. 6:24-26) God's divine action in Christ has done this. The Gentiles are no longer strangers.
This is cornerstone language is rooted in the words of Jesus to Peter in Matthew 16:18. Jesus is addressing the apostolic office of Peter, and not the person of Peter. The church is built on the confession of Jesus as “The Christ, the Son of the Living God.” The foundation comes from the preaching of the apostles after Pentecost. The apostles proclaimed Jesus as the crucified and risen Savior. God is the builder of His Church, through the Word and Sacraments.