According to Galatians 4:17, the Judaizers seek to arouse the Galatians to see association with them by shutting them out.  They shut the Galatians out so that those outside will clamor to get in.  A clever and recurring ploy in all sorts of groups.

Paul uses the verb ekkleisai (“shut out”), a transparent pun on ekklesia.  The church of Jesus has a table at the center; it is a place of hospitality.  A church that shuts out, or a party within the church that shuts out, has become an anti-church.