Church
Paul is writing to people who are used to worship being segregated into Jews and Gentiles. Jews worshipped one God; Gentiles worshipped many. Jews lived life following very strict rules; Gentiles sinned all they wanted and appeased their gods with sacrifices. So when the church came along, it was a hard transition for people to put aside old differences and worship Jesus together. However, Paul makes it clear all followers of Jesus belong to one church.
Churches can still be segregated places today, to our shame. We are all part of God’s family and should find ways to live that out.