On the other hand, communion is "closed" in the sense that it is an ordinance for born again followers of Jesus Christ, only.
What the leaders and the people at Mars Hill did today, around the Lord's table, was not an act of love toward the Muslim woman who was invited to the table. It was a supremely unloving and selfish act. For by trying to show the world how tolerant, ecumenical, and conversant they are with the practitioners of a godless religion (and the showiness of the timing, the 10th anniversary of the terrorist attacks did not go unnoticed by this writer), the church at Mars Hill set up the Muslim woman to blaspheme God. Instead of calling the woman to repentance and faith in the Lord Jesus Christ (Matthew 28:18-20; Mark 1:15; 16:15; Acts 17:29:31), they called her to the Lord's table in an unworthy manner (1 Corinthians 11:27-28). How crafty. How careless. How cruel.