... A closed Lord's Supper table is not a matter of arrogance. It's not thumbing one's ecclesiastical nose at the world. It is, rather, holding out hope to the world. It is holding the Lord Jesus Christ out to the world. A closed Lord's Supper table is holding forth the Christian religion, offering the saving doctrines of scripture and of the true faith to a world without Christ. It is extending the truths of the Reformed faith to other believers who are straying from the ancient paths; who are members of churches where the church leaders have moved the ancient boundary stones set up by our forefathers....
For the rest of the sermon on Lord's Day 28 of the Heidelberg Catechism, see here....