Where is the church?

Growing out of the Reformation is the contention that there are “two marks” of the Church: the Lord’s supper and preaching of the Word: Word and Sacrament. Some added “church discipline” as a third mark. The Catholic tradition has been “one, holy, catholic, and apostolic.” I wonder what you see as the necessary and sufficient “marks” of the church? A question that I’m sometimes asked is this one — and I’m interested in your answer: If the Lord’s Supper is so central to church definition, why does it not show up more often in the NT? (We have the synoptic account of the Last supper; we may have it in Acts 2:42-47 (breaking of bread); 1 Cor 11.)