In this age, the community of the messiah exists in concentric circles. The outer circle (circulus ad extra) is porous and visible to the world. The inner circle (circulus ad intra) is nonporous and impenetrable. The outer circle is the visible people of the messiah "built on the foundation of the apostles and prophets," the Old Testament Israel and the New Testament church. The inner circle is the elect "chosen in him before the foundations of the world." And, as in Jesus's parable of the wheat and the tares (Matt. 13.24-30), "both of them grow together until the harvest."
It is easy to enter the outer circle. No one can forbid it. One is born into it or one bids for membership out of personal desire or in response to an invitation. And there is a liturgical sign of entry. In Deuteronomy 28:9, directly after God says "The Lord will establish you as his holy people," he commands circumcision as a visible token of membership. Male babies were to be circumcised shortly after birth, and through them, the nation is circumcised. Circumcision was replaced by baptism in the Messianic, New Testament community. Members of the circle have public access to the benefits of the community.
It is impossible, by human effort, to enter into the inner circle (see Opening a Closed Circle, 83). Its members are elect by God. The language and benefits of the community are reserved for and active in the elect alone. They are the invisible community of the inner circle "born, not of blood nor of the will of the flesh nor of the will of man, but of God." The inner circle is the church militant (Ecclesia militans). It is the burning bush in which God dwells by the Spirit and every man, woman, and child is on fire.
It is impossible and evil to fix another's place on the inner or outer circle, aside from their making an overt declaration. And it can be challenging, in the day to day, to know where to place oneself.
This post is a work in progress. Its existence is to be a short, model ecclesiology, combining my model of "Saint Augustine's church", something on the two sacraments, and election.