If we think about a text such 1 Peter chapter 2, where Peter applies a whole series of titles that were originally given to Israel in the Old Testament now to the church – "You are royal priesthood, a holy people belonging to God" – we see that Peter is teaching a group of churches in a variety of regions, who are predominantly Gentiles, to see themselves as really the fulfillment of God's promises to Israel, and to recognize that that is their identity. That helps us now as we live this side of Jesus' death, resurrection, ascension, and outpouring of the Holy Spirit to recognize the significance of the very title "church." The Greek term "church" is ekklesia, and Jesus introduces it in Matthew 16 and mentions it again in Matthew 18. Really, it seems kind of out of the blue; it doesn't appear elsewhere in the four Gospels. It appears often, of course, in Paul's writings. But Jesus expected his disciples to know what he meant when he spoke of building his church upon the rock. He expected them to read that and to hear that in the light of the Old Testament usage of that same term – which is basically the Greek equivalent to the term of the "assembly" of the Lord – used in text like the text in the books of Moses that describe God coming down on Mount Sinai and Israel called into assembly of the very presence of God. That helps us to see what the church is about. It's not just a gathering of human beings. It's really the people of God that assembled in the presence of God. And of course Paul emphasizes that there is a unity to this people of God from old to new. There are definitely changes that come as a result of the coming of Christ. But Paul emphasizes in Romans 9 through 11 that theme of one olive tree into which wild olive branches, Gentiles, are now being grafted by faith in Christ. A single olive tree, a single people of God.